Refactor player connection (topfreegames#125)

* Refactor player connection

Those commits decouple the logic of reading messages from the
service/handler and delegates the responsibility for the acceptor itself
by implementing a GetNextMessage method. TCP Acceptor now parses whole
messages one by one from the stream, this way we ensure not to read
partial messages anymore.

Refactor player connection

Those commits decouple the logic of reading messages from the
service/handler and delegates the responsibility for the acceptor itself
by implementing a GetNextMessage method. TCP Acceptor now parses whole
messages one by one from the stream, this way we ensure not to read
partial messages anymore.

Adding etcd auth (topfreegames#118)

Fix pitaya client interface (topfreegames#117)

Allow client to customize handshake data (topfreegames#116)

Logging errors writing heartbeat

log before every heartbeat

improve agent logs

Change log level of GetSessionFromCtx

Trying again to fix dependencies