Add setEncoding method to connection
Update MqttClient to support publish encoding
Add tests for Connection#setEncoding
Fixed failing test due to the default being utf8 now.
Removed the use of 'call' inside Connection to pass the encoding.
Moved from null to 'binary' for specifying the binary encoding.
Merge branch 'set-encoding-v0.3.0' into v0.3.0-dev

Conflicts:
	lib/client.js
	lib/connection.js