move 'signature' out of the way
remove one of three hash representation
expand hash->function mapping
nice hashing interface
normalization between remaining two hash encodings
short cuts
re-expose pkcs1_digest_info parser

we don't really care about the native ASN algo. we care about a hash function we
know about here.
port certificate.ml

explicit hash->hashfn dispatch considered sooooo 2011...
Merge pull request #56 from mirleft/rehash

great work, works flawlessly here :)