Updated to gifsicle 1.70 and recompressed images.

Fixed King Sombra/black crystal1.gif, Pinkie Pie/teleportstart_pinkie_pie_left.gif, Pinkie Pie/teleportstart_pinkie_pie_right.gif, Rainbow Dash/rainboomtest.gif, Rainbow Dash/rainboomtest_trail_left.gif, Rainbow Dash/rainboomtest_trail_right.gif to no longer require a zero-duration solid colour frame so the final transparent frame was preserved (needed use of the restore background disposal method). The program will now log dropped zero-duration frames to console.
Changed content to be done on pre-build using the /MIR flag so that removed files will get deleted from output directories.
Added crystallized Twlight by supersaiyanmikito
First refactoring pass to reduce complexity of core pony update loop.