More tut.
Merge branch 'master' of github.com:felix-lang/felix

Conflicts:
	Makefile

CHANGE: doc generation is now done entirely in the Makefile
using built Felix tools instead of fbuild.

Tutorial indexes generated by tools are supposed to be
committed to the repository. The target gen-doc creates
these indexes. This should be run before committing
new tutorial pages so the upgraded indexes get committed too.

However, this cannot be done in a clean build, because
the tools for performing the index generation must be
built first. Therefore when copying the docs from
the repo to the release image, these indexes are
regenerated.

The check-tut target extracts, compiles, and checks Felix
code in the new tutorial after they've been copied to
the release image. The resulting files end up
in the release image but should not be installed.
This needs to be fixed!