Implement an in memory feature state behavior fixes #2

I saw this was up for grabs and I thought I'd take a stab at it.

A few things to be aware of:
- This the first time I've used git.
- I'm not familiar with MSpec at all but I tried to reuse as much a I could when defining the tests
- I haven't got a clear idea of you're code style (i.e. tabs vs spaces, naming conventions etc.)