[FEATURE REQUEST] Add EPUB (200MB) + MOBI output option

[KaMyKaSii]

This makes it easier for the same conversion to produce results that can be used on the Kindle both by SendToKindle and copied over the cable. The MOBIs will be generated from the same EPUB parts, so if the EPUB is split into three parts to comply with the size limit, three MOBI parts will be generated. I believe that this way it will not be necessary to modify much of the code. Thank you.