Reinstate the multiraft writeTask.

This gets us back to the state we were in before the move to etcd.
Add more comments about the raftReady/writeReady channel dance.
Merge pull request #144 from bdarnell/raft-storage

Reinstate the multiraft writeTask.
proto.Key and proto.EncKey for better static type checking!

Moved engine.Key to proto.Key and introduced a new proto.EncKey to
differentiate between unencoded keys and encoded keys. All engine
interfaces (lowest level) expected proto.EncKey. Higher level interface,
such as storage.MVCCC and storage.DB accept proto.Key.

These are now custom gogoproto types in the .proto files.
Added tip on forking with Go to CONTRIBUTING
Merge pull request #145 from cockroachdb/spencerkimball/key-encoding

proto.Key and proto.EncKey for better static type checking!
Merge pull request #146 from embark/embark/contributing

Added tip on forking with Go to CONTRIBUTING
WIP on txn clock uncertainty test