October 7th, 2017
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* New subprogram png2jpeg.
* Added --keep-extension.
* New conditions for converting only when a picture has no alpha channel: --if-opaque.
* Also converting only if size is exact: -if-size.

Sep 9th, 2017
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* Flag verbose (-v) implemented for printing all converted.
* Flah --keep-mtime to keep the original modification time.