Raise UnsupportedAlgorithm when initing HMACs
Merge pull request #326 from public/unsupported-hmac-hash

Raise UnsupportedAlgorithm when initing HMACs
restrict gcm tags to a minimum of 4 bytes in length
add note regarding not truncating tags
doc updates
prose updates for GCM tag
a few more doc changes to gcm tag info
Merge pull request #327 from reaperhulk/gcm-lower-limit-tag

Restrict GCM tag length to 4+ bytes
Merge branch 'master' into common-crypto

* master:
  a few more doc changes to gcm tag info
  prose updates for GCM tag
  doc updates
  add note regarding not truncating tags
  restrict gcm tags to a minimum of 4 bytes in length
  Raise UnsupportedAlgorithm when initing HMACs
provide text with unsupportedalgorithm error for hmac on commoncrypto
add tag length restriction to commoncrypto backend