Add setup instructions, fix tests, add rake tests


I added install instructions, then fixed the `user_spec` tests which were expecting a completely different stub than what was currently in there, and added :rspec as the default rake task. 

```
$ be rake
/Users/schneems/.rvm/rubies/ruby-1.9.3-p194/bin/ruby -S rspec -c -f progress -r ./spec/spec_helper.rb spec/secure_key_spec.rb spec/user_spec.rb
.............

Finished in 0.9041 seconds
13 examples, 0 failures
```
Merge pull request #2 from schneems/schneems/variable-key

Add setup instructions, fix tests, add rake tests