Indexer.Indexer supports UTF-8 paths
Index.WriteIndex supports UTF-8 paths

Have to do this in a kind of weird order, because of how the tests work
together.

See #6 and #8.
Index.Index(string) supports UTF-8 paths

See #6 and #8.
Index.BelongsToFile supports UTF-8 paths

See #6 and #8.
Index.VideoSource supports UTF-8 paths

See #6 and #8.
Index.AudioSource supports UTF-8 paths

See #6 and #8.
Track.WriteTimecodes supports UTF-8 paths

Fixes #6.

See #8.