Adds support for CBZ and EPUB input paths

[OhMesch]

Adds .cbz and .epub as valid path types when passed to mokuro or located within the --parent-dir structure. Partially addresses Issue " CBZ/CBR file support #9" but didn't want to make assumptions about CBR or introduce dependencies on proprietary format.

Added testing for .cbz and .epub inputs.

If vol1.cbz/vol1.epub are present in same dir as vol1/, will default to using just the vol1/, essentially skipping the zip types.

For .epub I'm ignoring any cover. images to keep generated outputs consistent.

Very happy to refactor to bring in line stylistically.