support for custom pixel aspect ratio #95
Description
hello! i'm currently using Libresprite to create the art for a game that i am developing. the game utilizes DOS-like graphics, specifically VGA mode 13h (whose color palate is supported in the editor), which utilizes non-square pixels (320x200 at 4:3, so PAR = 1.2:1) and thus requires a custom pixel aspect ratio. from what i have been able to find, this is a feature that Aseprite currently supports, but came after Libresprite was forked, and therefore is unsupported.
how the sprites appear in game at 320x200 (4:3 PAR=1.2:1):
how the sprites appear in editor (256x32, PAR=1:1):
how the sprites appear in game at 320x240 (4:3 PAR=1:1)
