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.
This was an unsupported build script to make building the library
with CMake look like building it with the Autotools. It hasn't been
maintained in a long time and we've had it marked as deprecated for
years.