feat(wrtag): add score-min config option

[yamhab]

This PR adds a configuration option, score-min, that allows the user to choose the minimum match score threshold in order to automatically tag a directory with a release (95% by default). I had it in the form of a percentage [0.0%-100.0%], as that's how scores are already internally represented. However, I suppose if it be preferred, it could also be a floating point number [0.0-1.0].

I was also thinking of sorting the configuration options in wrtag.go's Config and cmd/internal/wrtagflag/wrtagflag.go's Config() (maybe alphabetically, like in interface and documentation) and such that they'd be more consistent across the whole program, though I'd rather know if it should be done at all first.

Fixes issue #197.