Tag parsing

[FichteFoll]

There is a method to parse tags in a line, but it doesn't actually work because Tag.from_ass is unimplemented. (yeah)
Edit: has been removed in 0.5.4

Available options are:

1. Remove it and let users choose whatever they want to parse text lines (e.g. ass-tag-parser)
2. Use ass-tag-parser behind the scenes (not too satisfied with its current API)
3. Come up with a simple implementation on my own (seems like wasted effort when 2. exists)

[FichteFoll]

I have removed the tag-parsing code in 3f7e74a for now. I'll leave this open for any potential further debate in the future, though.

[moi15moi]

To parse tag, you could also look on how i did it: https://github.com/moi15moi/ass_tag_analyzer

It try to parse tags like vsfilter