Start cleaning up some macro names

This focuses mostly on otterylite_rng.h, trying to distinguish
"Ottery" keys and blocks and buffers from "ChaCha" keys and blocks and
buffers.
Clean up macro names in otterylite_digest.h

Give all the rotation functions better names than ROT, and put
"BLAKE2" in front of more things.
Untangle macros in fallback entropy gathering

These should be functions, and should use proper types.
Teach the fallback entropy grabber about more files