Fix some BSD Make issues.

This ignores the test sources, and specifies a default BINDIR for `make install`.
Decouple CommandHandler from Tokeniser.

The Tokeniser now returns a list of 'ready' lines from Feed, instead
of pumping them into a CommandHandler.  The TcpResponseSink now has
jurisdiction over running the CommandHandler.

This should make Tokeniser more testable.
Implement basic, but useful Tokeniser tests.

This is by no means a full test suite for Tokeniser.