BPWrite_c -> ctypes
XMLConfigTest.TwoIOs -> Test BP Writer 1

Continue refactoring IO, ADIOS classes

Passed ctest (MPI and nonMPI) excluding ADIOS1 engine, and Python bindings
HDF5, C bindings and C++ tests working
Introduced BeginStep EndStep functions
Renamed IO GetVariable/Attribute to InquireVariable/Attribute

Getting and defining available Variables at Open
Storing Variable position in Metadata, added to VariableBase
mpidummy: Added support for MPI_Reduce, MPI_Gatherv
Added utils and BPLS

Implemented basic buffer reading functionality
Added threading for bp serialization/deserialization
Refactored MPI functionality
Engine is now a reference
Initial Read API

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

Remove meaningless code(AddTransport which is not implemented yet) in
HDF5 test as well.

In this PR, I extend HDF5 native reader so that now hdf5 tests can read data
by selection(so called hyperslab selection in hdf5).

This PR also add testing for bp file name with path.

Since collective meta generation has not landed yet, I have to use
same attribute for all processes. Ideally attribute per process
should be unique to each other for testing purpose.

Testing and Examples issues after merging with master for conflicts
Fixing non-MPI issue
C enums and Fortran parameters now compatible

First working examples
To do:
Resolve conflicts
Add tests after merging with current master

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

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.

Added GetVariableBase* in IO needed by C bindings and real-time
applications, nullptr is a valid state in return.

Added c bindings test under testing/adios2/bindings/c
Updating ReadMe.md to include ADIOS2_USE_C for C bindings

signed char needed by int8_t in C bindings
Added tests

Refactored IO, Variable class due to common functionality

Wrapper classes CompressBZip2 and CompressZfp implemented
Under transform/compress and adding examples and tests
Added/Modified cmake files
Makign changes to cmake from PR review

To do:
Add more tests