forgetsy v 0.1

pinging @fancyremarker and @dblockdotorg for review.

This is a first round implementation of forgetsy. Please read the [README](README.md) to familiarise yourself with the aim of the library.

It should be considered unstable at this stage. There are still a few optimisations required before I would use this in production too. I also need to package it up so it can be easily included as a bundled gem, and so that redis is easily configurable.