Read ANSI files with different extensions

[Fixer-007]

I'm using it to view some of the art right now, there are lots of art packs that have .ANS files under many different extensions, that are not recognised.

Add some way, to recognise files as .ANS art ones without needing to rename thousands of files manually, maybe by reading a little bit of each file for signatures of such files if extension is not .ans, .ice, .zip, whatever you support.

[cwensley]

There is support for adding other extensions for each format, but there's no UI for that yet. Thanks for submitting the issue!