Negative TTL means 'dont store', zero means 'store forever', and positive means 'store for this number of milliseconds'
* Completed redis implementation
* Updated tests to include 'overwrite' (both cases) and redis database select
* Fixed some issues in the tests related to position of test.done() which only caused issue with truly async callbacks
* Bumped all module version numbers to 0.0.3 since previous commit had some mild changes in behaviour