Update version to 2.1 and derive version information from H5public.h, removing h5vers script and updating CMake and Java configurations.
Versioning:
Update version to 2.1 in H5public.h.
Derive version strings in H5public.h using macros.
CMake:
Extract version from H5public.h in HDF5config.cmake and HDF5AsSubdirMacros.cmake.
Configure README.md and CHANGELOG.md using CMakeLists.txt.
Java:
Generate H5Version.java from H5public.h for version consistency.
Update H5.java to use H5Version for version constants.
Removals:
Delete bin/h5vers script, previously used for version management.
