Fix loading in aegisub 3.0.X (I think)

aegisub.re does not exist in 3.0.x. If calling it fails, try to call
the wrapper script instead.
Use bracketed strings to avoid double escaping.

Thanks to line0 for bringing to my attention that I am an idiot.
Encoding changes.

- Auto-delete encoding script on non-windows platforms.
- Give encoding script a slightly more unique name to avoid overwriting
innocent files that happen to be in the wrong place at the wrong time.
- Log x264 output on non-windows operating systems because no cmd
window pops up.
Switch Aegisub-Motion.lua to compiled moonscript version.