Add empty, xxx, anglequote and shouty transforms

The empty transform is fer emptyin' out th' translations in a .po file.
Sometimes that's 'elpful.

The xxx transform adds xxx before and afterr a strin'. I took inspiration
from podebug fer that one.

The anglequote transform is like th' bracket transform from podebug, but
it uses unicode anglequotes which I thought warre more intarrestin'.

THE SHOUTY TRANSFORM MAKES THINGS IN ALL CAPS.

One intarrestin' thin' is that ye' can chain transforms. Want a shouty
pirate? No problem.
Update CHANGELOG