Add Unicode aware Capitalize filter

[gnunicorn]

refs #11

[gnunicorn]

@johannhof I wanted to create more filters, but this will be a problem every time if I do them as one PR at a time, as they all modify the same line. Should I just use one branch make one filter per commit and then one bigger PR instead maybe?

[johannhof]

@ligthyear sounds like a good solution 👍

[gnunicorn]

will superseed this one soon.