* basic support for SSA formatted subs. (disable with --no-subsdec-formatted option)
* changes to freetype renderer to support the font color, size and alpha options of text_style_t (other options are possible, just not implemented yet. Full text_style_t support requires a more advanced renderer though. )
* changes to modules to support text_style_t instead of the old sub options.
* Some changes to subsdec to only iconv to UTF-8 if source is !UTF-8.

refs #82

not supported are style runs (styles on substrings).

Fixes subtitles detection from within folders with non-ASCII names when the local encoding is not UTF-8 (closes #536)

The download specific functions should maybe be exported (i don't know if
other modules would need to download files to disk)

zorglub: could you have a look ? this solution doesn't seem right to
me because we "loose" some of the calls to the interaction system if
they're sent at the wrong moment.

* Reduce vlc_object_find calls