Modularised as CommonJS with Browserify

Using Karma for test running with Browserify, producing a debug build
too. A couple of breaking API changes: `SirTrevor.DEFAULTS` is now
`SirTrevor.config.defaults`, and `SirTrevor.instances` is now
`SirTrevor.config.instances`.
Merge pull request #260 from madebymany/commonjs

Modularised as CommonJS with Browserify