Callback Signature classes extend Operator
Operators can be used per Variable, IO or Engine

Continue refactoring IO, ADIOS classes

BP3 Deserialization:
Getting subfile seeks and intersection info
Set host language in bindings for row-major and zero-index info

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

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

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

Fixed conflicts for clean compilation
Fixed clang-format
Adding free in C example

Added working example examples/hello/bpWriter/helloBPWriter.c
Changed Engine signature to resolve Write void* at runtime (required by
C bindings).

To do:
CMake infrastructure
Testing

Makefile compiles

To do:
CMake infrastructure
Verify struct adios2_Engine  forward declaration
Add 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

Removed ADIOS copy constructor explicitly, as it wasn't allowed by clang
compiler in testing/xml/TestXMLConfig.cpp

Using more portable preprocessor definitions to avoid warning on Windows
for ctime and fopen

Introduced std::throw_with_nested for bad_alloc in STLVector Capsule

Removed std:: in C function calls to avoid confusion with actual C++
only calls

Checking std::ios_base::failure exceptions
IOChrono is off by default, each owner turns it on explicitly
Modified FileDescriptor and FilePointer destructors
Added Tests BPWriteRead for stdio and fstream
Removed IO AddTransport with vector (shoud have been there?) to enable
AddTransport in Tests

Keep only std::map<std::string, std::string> initializer list.
Corrected examples. 

Initial implementation of XML running with helloBPWriter example
Corrected bug in ADIOS.cpp when detecting IO in ConfigFile

m_Name must a string object not a const reference. 

Python bindings running but not printing values with bpls. Min and Max
captured correctly.

IO SetParameters and AddTransport will accept vector and map

Variable.cpp and Variable.tcc for complete separation of core components
in the public include

To do: 
Debug hello_datamanWriter non-MPI version

bool flag checks are implicit
Removed single letter enums in ADIOSTypes.h
All enums are enum class in ADIOSTypes.h using CamelCase
ADIOS uses delegating constructor
Using return type of emplace for IO (in ADIOS) and Variable (in IO)
Removed all base class include from inl template file