Release 1.21.1

Updated binaries for all platforms to latest 1.21.1 release. Major changes since 1.19 are:

• Background layers accept full bitmaps in addition to classic tiled backgrounds. Now it's possible to develop games such as Worms, that use complete bitmaps. Check this Facebook note for full details.
• Enhanced input: now it's possible to set a user-defined callback to get all SDL events generated inside the window. This allows bypassing the standard input model of tilengine and use another keyboard layouts, mouse, etc. Chek this Facebook note for full details.
• Several bugfixes to errors found by GitHub user @bhelyer, related to persisting states between fullscreen/windowed mode toggles and fedding resource loaders with invalid or unexpected data format. Check GitHub commit for full details.