Proposal: Change CLI to accept entry files (similar to the duo itself)

[dominicbarnes]

I don't know if I'm the only one, but I find the current CLI a little confusing to use at first. So much so, I've actually created my own duo-based test-runner at dominicbarnes/duo-test, and I think the interface is a lot more intuitive, especially in comparison to the duo core CLI.

I figured I would at least propose my idea, but I'm totally fine continuing to just use my own runner at this point. (the only real gap it has is that it doesn't do saucelabs testing)

Basically, my CLI takes a variable number of arguments, where each is an entry file that is added to the resulting HTML. (or test/*.js as the default) It uses dominicbarnes/duo-serve under the hood to auto-rebuild. (rather than incorporating a build command into the CLI)

# run phantomjs testing against test/*.js
$ duo-test phantomjs

# start server for browser testing of test/a.js and test/b.js
$ duo-test browser test/a.js test/b.js

My main issue with the current API is the complexity of adding custom build commands, as the default is seldom usable for me. Plus, making the command mirror duo itself should make it easier to start using.