docs(crypto): fix E400, E405, E410 documentation issues
- E400: add module doc comment to wycheproof.mli
- E405: add missing doc comments for public values in crypto_pk.mli,
crypto_rng.mli, crypto.mli, wycheproof.mli, and pk sub-modules
- E410: fix doc style (arg counts, name format, trailing periods) in
entropy.mli, getentropy.mli, urandom.mli, chacha20.mli, uncommon.mli