Replace with std::stringstream implementation put for convenience
in XdmfStringUtils.hpp. Added a test as well.

Previous implementation of C interface passed raw pointers
up to user and it was unclear and inconsistent who owned the pointer
leading to bugs. The previous implementation lead to creation
of many copy constructors, many of which had bugs.

Now we pass opaque pointers to C which the user is *always* responsible for
freeing.

Remove broken copy constructors.

Update C tests so that all pass valgrind memory leak checks.

Changes from ARL's Repo (C Wrappers, DSM rework, Custom Types, Templates, GridControllers, TIFF integration, XdmfAggregate)

Rework of HeavyDataController and HDF5Controller to remove extra code and move HeavyDataController away from being too dependent on hdf5 style
XdmfFunction now supports negative numbers in addition to the - operator
Reworked the interaction between array references and reading
Cleaned up some warnings that showed up in pedantic
Adjusted mpi tests to test against the MPIEXEC variable as opposed to hard calling mpirun
Still needs to be changed to work better with Cray mpi style execution
Updates to XdmfArrayType to allow for signed and floating point checking
General test and Documentation updates

wrapped function and subset into superclass XdmfArrayReference to allow for easier implementation of new array references