Lots of improvements!
- config overrides for binary paths, cache dir
- url_only param
- Ghostscript check
- Split conversion into 2 commands, instead of Imagemagick calling GS implicitly. This allows us to set a bunch of GS options that normalize colorspaces, as I was having lots of funky issues with wrong colors when using just convert.
Readme update
Better Ghostscript test
Merged in @timkelty fixes
Merge branch 'timkelty-master'