#195 support for couple more file formats: mpo, ass

[Gleb Smirnoff]

Please, add support for couple more file formats:

1) .mpo - known as "multiple picture object", produced by some Japanese cameras. Basically it is several jpegs in one file.
2) .ass - subtitles format, AFAIK originating from Matroska.

These patches have been around in the FreeBSD port for a while, originally requested by our users.