1.2.0

Handles the following:

* `Externalize` has been deprecated in favor of `alias` (#69)
* Allow `external` to use module names, in addition to file paths (#68). Waiting on Browserify changes for this to actually work.
* Much improved docs (#67)
* Allow non-files to be ignored (#50), via @joshuarubin

Could I trouble @shama and @bclinkinbeard for a review? Thanks!