Pysodium

added a bunch of ristretto255 functions and included license in the manifest.

some fixes, and some new functions added. thanks to all contributors!

This release brings stricter parameter checks, secretstream functions, and a few other improvements and fixes.

This is a release on github, pysodium is normally released on pypi, but from time to time there's also a github release. this is such a release. it mostly contains bugfixes and a few new functions added by kind contributors.

fixes bugs with older libsodium versions

this is a new release with
- new functions for crypto_box*_detached,
- crypto_box*nm,
- the easy functions have been merged into the "non"-easy ones. they don't provide any extra feature for us, as the crypto_box interface was already hiding away the padding.
- wrappers for crypto_aead_chacha20poly1305_ietf\* have been added.