made kx.observer.subscribe and kx.observer.unsubscribe chainable and gave them an optional callback which gets the original return value as argument, closes konfirm/konflux#10
kx.observer.subscribe and kx.observer.unsubscribe now use the same regex to split an events string
Merge pull request #11 from daanvanham/develop

kxObserver subscribe and unsubscribe are now chainable and changed to regex for splitting the events string