Add a protocol buffer stream to the FileWriter

- also reuse the protocol buffer instead of generating a new instance each time
Clean up the Message string setter functions since strings are immutable
Make the buffer large enough to hold the max message and header structure
Add TcpWriter and updated FileWriter support for protocol buffer streams
Remove the debug dump and include the TcpOutput plugin config
Incorporate code review feedback

- corrected createProtobufStream signature
- removed duplicate stream header generation code
Merge branch 'features/protobuf-output' into dev

Conflicts:
	pipeline/config.go
Merge branch 'dev' of github.com:mozilla-services/heka into dev

Conflicts:
	pipeline/config.go
	pipeline/inputs.go
	pipeline/outputs.go