Subtitle fixes and new formats

Added support for multiline subtitles. (h/t J Larmour)
Fixed small timing error. (h/t R Dixon)
Fixed leading hyphens for change of speaker
Added --subbreak to force use of line breaks from subtitles file

Added 2 new subtitle formats and corresponding options:

--subcolour uses colours (if present) to denote change of speaker in
a subtitle.  Also uses line breaks as specified in subtitle file.

--subbasic uses line breaks as specified in subtitle file, but does
not denote change of speaker.  This is should be same format as Flash
player on iPlayer site.