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
Decay should delete terms that decay to zero
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
Prevent errant karma from within a longer string
Merge pull request #10 from erikogan/negative-karma-decay

Negative karma decay
Merge pull request #11 from erikogan/decay-cleanup

Decay cleanup
Move the terminator variable to a private method, with a comment explaining its purpose
Merge pull request #12 from erikogan/errant-karma

Prevent errant karma from within a longer string