WME Subtitles

I've ported Mnemonic's subtitle code from WME1 and tweaked it to go with our style and conventions.

This seems to work well enough with both autodetected and 'regular' subtitle files from my demo game (mov_test from my repo wme_testsuite)

Comments added, to the best of my understanding (this bit is off the 
original - it could probably also benefit from some slight refactoring, 
but I don't want all the fun for myself :-).