Add tests for decay when the term has a negative value
Upgrading karma for terms with negative karma was not adding actions for them correctly
Fix the example upgrade_modified lambda to:

* Not throw a NoMethodError
* Correctly handle negative karma
Update the key used to indicate decay is up-to-date

This will cause anyone using decay in the broken version to acquire the missing actions
Merge pull request #10 from erikogan/negative-karma-decay

Negative karma decay