Documentation improvements

Hi Osawa-san,

This has a number of small changes, mainly related to documentation, but also to get it CPANTS-clean.

I was going to switch the builder, but noticed you've used Milla on more recent dists, which I'm not familiar with.

I'd be happy to do a release, if you want to give me co-maint. My PAUSE id is NEILB. You happy for me to switch to Dist::Zilla, if you do give me co-maint?

Cheers,
Neil