added bower to install polyfills for testing
Merge pull request #34 from garthenweb/karma-polyfills

added bower to install polyfills for testing
implemented .on(), .off(), .once()
added events to available methods section in readme
use event.target instead of event.currentTarget
added comments for event code
fixed broken tests
use es6 WeakMaps for event references
added polyfill for WeakMap