CommonJS Support

Hi, this PR adds CommonJS support to scribe, so you can do require('scribe') in Node, and in return, have that browserified. The main work is done in a plumber plugin I wrote which uses https://github.com/gfranko/amdclean and then pushes the result to the module.exports. https://github.com/britco/plumber-umdify.

To build the CommonJS version, you run `plumber build` usual.

Then, to require the module you would put in your package.json something like:
`"scribe": "britco/scribe.git#dist` And then you just add a require like you normally would:

````
Scribe = require('scribe')
ScribePluginBlockquoteCommand = require('scribe/plugins/blockquote-command')
scribePluginToolbar = require('scribe/plugins/toolbar')
scribe = new Scribe($(".scribe")[0])
scribe.use(ScribePluginBlockquoteCommand())
````
Although my hope was you guys could publish the module to NPM, so you don't need to pull it from git.

Also I read over the contributing guidelines, but I wasn't sure how this would play with all of them. Like it's not a typical release, it's just a different format. Should I bump the version number still?

#83
#77