Addition of WRatio

[guwidoe]

This PR attempts the addition of all functionality required for the addition of WRatio which includes:

• token_ratio
• partial_ratio
• partial_token_ratio
• wratio
• and some lower-level dependencies of these functions.

Additionally, lots of test cases were added. (Many of which don't pass yet (Sometimes the tests themself make wrong assumptions, but they are a good base for further debugging.)

This PR should not be merged yet.

One major issue is that, because the ratio function returns in the range from 0-1 and the other newly implemented ratio functions return between 0-100, like in the C++ implementation, hence the score_cutoff parameter doesn't work properly yet.

However, with score_cutoff set to 0, the functions seem to return the same values as in the C++ reference implementation.

I have opened this PR because I'm not sure if I will have time to further work on this - I think the current, very sloppy state of the implementation in this PR is already sufficient for my use case for now.

[maxbachmann]

@ljnsn is currently looking into porting the remaining functions as well, so this could help him.

The partial_ratio implementation here appears to mistakenly implement the token_ratio instead.

[guwidoe]

Thanks for the hint, I will look into it as soon as I have time!