png slow with mobi

[axu2]

Should use gif instead of png

Since kindlegen converts png to gif which multiplies the processing time. As noted in

• #41

On that note should probably add an option to match output format to input, since a png source converted to jpg can actually make things bigger and vice versa. I bet that's what's happening in

• #349

EDIT:

Was as simple as adding this:

                # self.image.info["transparency"] = None
                self.targetPath += '.gif'
                self.image.save(self.targetPath, 'GIF')

GIF is problematic on Scribe though.

• #665