Parser: ignore single quote (ugh) HTML fragments too.

This intentionally introduces a bug (uh, feature, that is) where
mixed-quote fragments will be ignored. I don’t foresee that being a
problem. (Don’t worry, hindsight will be 20-20).

Anyway, the updated unit tests pass, so it must be OK.
Readme: a few small updates
Parser: Allow an array of textdomains to be passed to the constructor
Ignores: add two functions to the lists