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.

This change replaces xpath_node_set single element storage with a
single-element array in hopes that this would silence Coverity false
positive about getting a singleton pointer.

Additionally, it refactors _assign member to unify small and large
buffer codepaths since they are basically identical.

Fixes #233 (hopefully)

Intel compiler by default sets flush-to-zero flags which causes our
denorm test to produce 0.0. So make sure that denorms work on FPU before
testing the string output.

Fixes #218.

Instead of hardcoding SOVERSION, use CMake variables to set it up.

Closes #220.

* Visual Studio Natvis visualization

* Changed string format to remove separate natvis file for wide character mode

* Display any node type with name and value if any of them are available

On some Debian systems it looks like we *can* open the current folder as
a file and read its contents, but parsing the result produces an empty
document. We now handle this case as well.

Fixes #225.

Fixes #224.

This makes sure the contents of tests/data/ folder does not go through
newline conversion, which breaks tests that rely on some files having LF
and some files having CR+LF.

Fixes #222.

It looks like zipfile module by default uses the permission mask 0,
which after unpacking on Unix-based systems leads to the files being
inaccessible.

We now explicitly set file mask to rw-r--r-- to match .tar.gz defaults.

Fixes #217.

- Up to now, the libdir was hardcoded to "lib" inside pugixml.pc and
  the install directory of pugixml.pc was "lib/pkgconfig"
- Adds support for lib and lib64 by using CMAKE_INSTALL_LIBDIR variable

This also bumps the minimum CMake version to 3.0 (from 2.8.12).

This is implicitly true due to the following section, but that was
written before C++11 so this does deserve a special mention in ranged
for section as well.

Fixes #210.

This setup can interfere with existing workflows in two ways:

- If the target application used CMake and configured custom postfixes,
this change would override them

- If the target application did *not* use CMake, it'd have to abide by
these conventions even if the target configuration used is unexpected -
for example, the default "preferred" configuration is frequently
RelWithDebugInfo, not Release, which now has a postfix.

Fixes #198.

This might have helped a bit with confusion in #195.

Add example code

We no longer need to specify the license boilerplate verbatim since we
have a separate file.

Also rename LICENSE to LICENSE.md

Also fix two http → https occurrences.

There's really never a reason to *not* want this installed. If an option
is needed to specify installing in a versioned subdirectory, this option
should be explicitly described rather than hidden in something else.

As an added bonus, this makes the CMake install code slightly *less*
complicated.

We need bad_alloc that lives in <new>, not <exception>.

pugixml.hpp wasn't including the <exception> header in this build but
test code needed it.

gcc-8 produces "attribute directive ignored" warning for
no_sanitize("unsigned-integer-overflow"); at some point gcc will
introduce integer sanitizer support and we'll have to do this all over
again but for now just don't emit the attribute.

Mention ubsan fixes; these fixes probably fix compact mode on some
64-bit architecture where unaligned pointer reads aren't valid as well
but it's probably not very relevant...

Several tests got the buffer size wrong when sizeof(char_t)>1, and one
test didn't meet the carefully tuned allocation criteria under compact
mode due to the hash table usage and had to be changed a bit.

We were using << compact_alignment_log2 instead of * compact_alignment
for symmetry with the encoding where >> is crucial to keep code fast and
round to negative infinity.

For decoding, the results are the same and any reasonable compiler
should convert *4 into <<2 so just use a multiplication - that doesn't
trigger UB on negative numbers.

We were using allocate_memory to allocate struct xml_extra_buffer that
contains pointers; with compact mode, this allocation can be misaligned
by 4b with 8b pointers; fix this by manually realigning the pointer.

We were misaligning document data on 64-bit platforms by placing 8b
pointers at 4b offsets; fix this by reserving a full pointer worth of
bytes for page marker.

Define noexcept using _MSC_VER instead of _MSC_FULL_VER (first release
of MSVC 2015 should have it), remove redundant PUGIXML_HAS_NOEXCEPT and
define PUGIXML_NOEXCEPT_IF_NOT_COMPACT in terms of PUGIXML_NOEXCEPT.

Still trying to decide if the next version should be 1.9 or 1.8x and
what other changes need to go in.