Add keymaster

Source: https://github.com/madrobby/keymaster/blob/64fc7e56aa97efd9a1802a15e773fa98d3903372/keymaster.min.js  
Package: https://github.com/madrobby/keymaster/blob/64fc7e56aa97efd9a1802a15e773fa98d3903372/package.json + filename