Added a stopCallback method.

I needed this because my knobs were being dynamically unloaded from the page yet they update callback kept running.
Added a stopInterval function.

if the knobs are ever unloaded the callback still runs and gives an error.
Merge pull request #25 from seanmadden/master

Prevent intervals from attempting to execute callbacks after knobs have been unloaded.
Create README.md
removed animation interval
Removed legacy code and updated minified script