Tidy format handling.
Refactor walk logic.

The walk logic to find a project descriptor is now performed before the
command line options are configured which allows the options to be
altered depending upon the project context.
Make typeforge(1) help adaptive.

This means that when it is executed outside the context of a valid
typepress project only a minimal help output is generated and only the
init command (and related options) are available.

Also improve handling when an unknown command is specified.