added HMAC key version, SigningException, and tests for HMAC key version
Merge remote-tracking branch 'upstream/master'
updated according to Cory's comments
removed keyversionmatter byte array from HMACKeyVersion according to Cory
's suggestion
Merge pull request #19 from jmaheswaran/master

Added HMACKeyVersion, HMACKeyVersionTest, SigningException, HashKeyVersion
Add protocol buffer definitions for key version.
Removing placeholders.

- The protobufs complete the picture.