Adds test documents for extensions.
Improves extension code to use proper objects (like engines).

Removes output annoyance with makeindex.
Fixes issue #26 -- bibtex extension is now only rerun when necessary

Shrinks the unnecessarily huge test bibliography file.
Log clearly states so if there was no output of a subprogram.

Regards issue #13; it is important to tell the user that everything went fine, too!
Graceful recovery & user information in case daemon mode is requested but listen gem is not installed.

Regards issue #22.
Addresses issue #27 -- tikzext and gnuplot can now work in parallel.

Readme updated.