Feature request: Allow XPM file format

Feature request: Allow XPM file format

I am missing "xpm" from the list of file formats allowed in art submissions.

For those who don't know xpm: It is a paletted image format where the image is defined by a string array using C syntax. The format was designed for 8bit icons and the typical tool to create an xpm is a text editor.

Of course it is possible to convert from xpm to png, but in some sense such a conversion is lossy:

- An xpm can contain C style comments.

- The palette keys (substrings, usually of length 1) can be descriptive.

- The palette does not have to be injective: It is possible to use different keys for the same colour and thus convey more information. For example, one can thus distinguish a black outline from an area which just happens to be black but plays a similar role as some orange area.

These are corner cases, but they suffice to make the xpm version the source of the image, a GPLed png obtained from such an xpm would not be distributable without the xpm alongside.

I have some old stuff I intend to submit. It's all xpm and all above possible reasons for lossyness do occur.