Use a 2-pass approach to generate ADIOS2.config.  The first pass
generates the configurable options in the header and the second pass
configures them.  This allows for consistency in the options used and
thier ordering with respect to where they're used elsewhere.

Redesign the logic for C binding test with google framework.
In the future we should also add validation for binding tests.

Auto-detection of language available doesn't correctly work in CMake so
just explicitly default to OFF here and error out if set to AUTO.

Subroutine based, calls the C bindings using opaque pointers
Working helloBPWriter_f in MPI and nonMPI examples
Separated MPI and nonMPI interfaces in Fortran and C
Passing character array by trimming and adding char(0) null terminated

To do:
Add testing

Fixes #222

TO achieve this goal, GoogleTest.cmake is extended to allow
exec_wrapper and SmallTestData.h now would generate data based on
step&world_rank&world_size.
ADIOS2ADIOS1WriteADIOS1Read2D1x8/2x4/4x2 now runs in MPI.

Builds libadios2_c.a and libadios2_c.so 
Verified with and without MPI
Added nonMPI hello bp write example
Added new ADIOS2_USE_C ON/OFF cmake argument

To do:
Add C tests and cmake support for the latter

Fixes #154

Fixes #196

Fixes #153

Fixes #175 (again)

Fixes #175

* Add initial python support to CMake build

* pybind11 2017-04-07 (1df91d36)

Code extracted from:

    https://github.com/pybind/pybind11.git

at commit 1df91d36cfa997c8987889234304ea5e37cc3e68 (v2.1.1).

* Build python bindings with cmake

* Adjust for adios2py -> adios2 module name