appending the suffix to the build product need not be a function of
whether CMAKE_CONFIGURATION_TYPES is set.  for example, having two ninja
build trees---one for debug and another for release---is a fine use-case
for USE_POSTFIX.

This change adds format_attribute_single_quote flag that uses single quotes (`'`) instead of double quotes (`"`) for formatting attribute values.

Internal quotation marks are escaped using `"` and `'`.

std::random_shuffle is removed in current standard

use <random> 's generator and std::shuffle instead

Also split one-liner if/for loops for better readability and coverage.

Remove contrib folder

This change removes contrib folder since it doesn't seem very useful;
Natvis scripts can and should go to scripts/ along with project files.

foreach.hpp is supporting a severely outdated BOOST_FOREACH construct;
in C++11 ranged for loop can be used with xml_node::children/attributes,
and BOOST_FOREACH can work with these as well.

foreach.hpp was also accidentally licensed as public domain which isn't
very helpful when the actual library is MIT. We could fix the license
but it seems better to just remove it.

Fixes #264.

Also fix code style.

Includes wording fixes and format_skip_control_chars

format_skip_control_chars

We now have two tests: one tests behavior when we run out of space when
appending the node set (in which case the append fails), another one
tests behavior when we run out of space when filtering the node set (in
which case the set still contains redundant data).

Given an unsorted sequence, remove_duplicates would sort it using the
pointer value of attributes/nodes and then remove consecutive
duplicates.

This was problematic because it meant that the result of XPath queries
was dependent on the memory allocation pattern. While it's technically
incorrect to rely on the order, this results in easy to miss bugs.

This is particularly common when XPath queries use union operators -
although we also will call remove_duplicates in other cases.

This change reworks the code to use a hash set instead, using the same
hash function we use for compact storage. To make sure it performs well,
we allocate enough buckets for count * 1.5 (assuming all elements are
unique); since each bucket is a single pointer unlike xpath_node which
is two pointers, we need somewhere between size * 0.75 and size * 1.5
temporary storage.

The resulting filtering is stable - we remove elements that we have seen
before but we don't change the order - and is actually significantly
faster than sorting was.

With a large union operation, before this change it took ~56 ms per 100
query invocations to remove duplicates, and after this change it takes
~20ms.

Fixes #254.

This test is very sensitive to the particular implementation of union
aggregation; for now lets disable this.

We need a more robust way to test union allocation failures.

This does not change the result of a union operation [substantially], but
it means that we now give a list to remove_duplicates that has more natural
ordering.

If remove_duplicates didn't sort the array, we'd have union operations
resulting in a consistent predictable order.

Contributes to #254.

We now have a ${LIBRARY} variable that we can either use directly or in
a foreach loop to be able to process either pugixml or pugixml-static
and pugixml-shared targets.

Also fixes incorrect shared library assignment when
BUILD_SHARED_AND_STATIC_LIBS is defined, and only links the static
library in for make check.

Change confusing wording: null nodes compare as equal to null handles, the previous wording implied that each null handle is unique

This may or may not make it more clear that pugixml.cpp has to be
compiled - either as one of the projects or as a standalone project via
CMake et al - for it to work by default.

Fixes #256.

Fixes an installation problem in Nix packages, as non-FULL variables are
already absolute paths in this case.

This allows us to reuse this code for MinGW builds.

Additionally disable coverage step for Linux clang - it looks like
Travis has a mismatch in the version of gcov info between clang and gcov
which causes gcov to crash - somehow this crash isn't picked up as a
build error.

We are currently only testing UTF8 mode which means we don't have code
coverage for some UTF->UTF decoding paths.

This is a dummy commit to trigger codecov build

Use cygwin to build coverage build and upload coverage data to codecov.

The behavior on Linux is very different between kernel versions, and it
triggers an unexpected OOM during sanitizer runs because somehow the
size is reported to be LONG_MAX. It's not clear that it helps us cover
any paths we don't cover otherwise - it would be nice to be able to test
failing to load a multi-gigabyte file on a 32-bit system, but we can't
do this easily atm anyway.

This commit changes sanitize configuration to fail on the first error
and ignore floating-point division and overflow "errors" that trigger
when we test the corresponding functionality. This makes it possible to
run this on all commits - if new UB or memory safety issues are introduced,
asan/ubsan will catch them.

We had a few places in test code and library source where we used an
implicit float->double cast; while it should preserve the value exactly,
gcc/clang implement this warning to make sure uses of double are intentional.

This change also adds the warning to Makefile to make sure we don't
regress on this warning.

Fixes #243.

This change modifies the table entries for ctx_special_attr to treat TAB
character as special, which makes the output code escape it.

Before this change, trying to use TAB in an attribute value would output
it verbatim; during subsequent parsing, pugixml - and other compliant
parsers - would apply attribute-value normalization, turning the TAB
into a space and losing the original value.

Using 	 fixes this; if an input document has 	 in an attribute
value, that gets unescaped into \t during parsing and escaped back into
	 during output, which means we can now roundtrip values like this.

Fixes #242.

Coverity hits a similar false positive to what clang static analyzer hit
- it assumes that since optimize() checks _right for being nullptr,
optimize_self() might hit _right=nullptr in the ast_op_equal case which
is impossible.

Contributes to #236.

The following warning is removed:
Visual Studio 14.0
1. warning C4275: non dll-interface class 'std::exception' used as
   base for dll-interface class 'vtkpugixml::xpath_exception'

clang doesn't understand the invariants guaranteed for specific AST node
types and, when seeing null pointer checks in optimize(), assumes any
pointers in the node might be null. Work around this by adding explicit
- redundant - null pointer checks.