Add link to contributors page on GitHub.
Add example for test compilation with the library.
Fix BSA header in the features.hpp template file.
Change copyright holder in version.hpp to BSA.

Even if started earlier, version file should have the latest copyright
holder.
Remove all rights notice, but keep contact information.

Copyright on BV parameters is held by I. David Brown.
We still want to state what changes were made.
Avoid using ICSD cif files in unit tests.
Support alpha and beta pre-release markers.

For alpha or beta releases DIFFPY_VERSION is decreased by 500.
This ensures version number will be higher in actual release.
Ensure features.hpp is built with the lib alias.