Improved documentation

Changed how to run tests; can now simply do `npm test` without having to install mocha globally.
Minor adjustment to usage example
Added some clarification to usage example
Eliminated async as a dependency; now only a devDepedency.

Removed underscore as a dependency entirely.
Merge remote-tracking branch 'remotes/upstream/master'

Conflicts:
	lib/index.js
	package.json
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