Minor change for JSHint.
No need for intermediate callback function -- pass callback directly.
Minor factoring of queue flush routine.
Skip the tests that need a bit more setting up.

Note that these tests do pass, it's just that they need a bunch of messages in SQS and at the moment they are set up outside of the test itself, which is not good.
Switch out underscore for lodash.
Upgrade some components.
Get everything NPM-ready.
Add more information about how to use the library.