Subtitle fixes and new formats

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

Added 3 new formats and corresponding options:

--subcolour : Uses line breaks as specified in subtitle file and uses
colours (if present) to denote speaker changes.

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

--subcompact : Uses line breaks as specified in subtitle file and uses
hyphens to denote speaker changes