Change some docstrings & indents in extras/

Some (not all) docstrings were changed to create summary lines with max 72 characters.
Instructions in extras/vba.py were edited to include mercurial and autoconf info and commands for running ./dl-libs.sh, which fixes #150 and fixes #151.
extras/gfx.py was edited to have 4 space indents instead of 8 space indents.