Adds release info for 2.1.0

[bmribler]

• Changed 2.0.0 release page to 2.1.0
• Started using dynamic release version and date
• Updated the New Features page and the Software Changes page

---

Important

Update release documentation for HDF5 2.1.0 with dynamic versioning and new features.

• Release Information:
  • Update release page from 2.0.0 to 2.1.0 in hdf5_2x.dox.
  • Use dynamic version and release date in hdf5_2x.dox.
• Documentation:
  • Update release_specific_info.dox to include new features and changes for 2.1.0.
  • Rename hdf5_2_0.dox to hdf5_2x.dox and update content for 2.1.0.
• Aliases:
  • Add SRCURLALL alias in aliases for dynamic branch URLs.
  • Update SRCURL114 to SRCURLALL in hdf5_1_14.dox for release document links.

^{This description was created by for 628a42a. You can customize this summary. It will automatically update as commits are pushed.}