Merge pull request #90 from Ghabry/development

8bit PNG: RPG Maker always uses palette index 0 as transparent color
Enable SDL_mixer in configure.ac
Merge pull request #91 from fdelapena/master

Enable SDL_mixer in configure.ac
Merge branch 'master' into development
Terminate player if image is missing instead of rendering garbage (fixes #32).
Better fix is welcome for later but good enough for 0.1
Exit player when image is missing (regression fix for #32)
Better solution will be added later...