Add composer repository

[timiwahalahti]

Hi,

Since this plugin isn't in w.org plugin repository, it can't be used with composer and wpackagist.org mirror. Composer repo would be awesome, and it's simple to made with packagist.

[NateWr]

Hi @timiwahalahti,

This isn't actually a plugin. It's a library that you need to include in your own plugin or theme. Still, a composer.json file would be neat. I don't use composer much, but would be open to a PR for sure.