error out when config.ciphers is empty
by default, prefer (perfect) forward secure ciphers, but allow all supported ones
introduce type hash
provide get_mac and get_hash, move digest_size around
use hash in configure, instead of Packet.hash_algorithm
provide hash_algorithm_of_tag and reverse functions (mac_tag_of_hash_algorithm, hash_tag_of_hash_algorithm)
use Asn_grammars.pkcs1_digest_info_of/to_cstruct directly instead of using wrappers in crypto now that hashes are real
use hash in SignatureAlgorithms (instead of Packet.hash_algorithm)
adjust test cases for last change
fixes to compile changeset
Merge pull request #189 from mirleft/hash

Hash