parser: catch more parse errors.
cli: catch errors in scandoc
clarify documentation that only PDFs are currently supported as input files
cli: small tweak to usage
setup.py: Extract version from lib version.py file
cli: fix version output

Use pkg_resources.
make: add update-version target

Creates the version.py file from the calculated VERSION
make: update lib version when making debian snapshot
cli: tweak command aliases
make: add release target.

Expected to be run as so:

  make release V=1
update todo
make: commit updated version on release
Update version for release 0.5.3.
Update version for release 0.5.2.