Make change event always fire as the user interacts with the knob:
- touch
- wheel
- typing (by binding to the "input" event)

Previously, typing did not update the knob until focus was lost (and
no change event was fired), and
using the keyboard arrows did not fire any change events.

Also move event triggering to val() and change() so it works always
in the same way and less duplication exists.
Merge pull request #140 from amuino/consistent_change_events

Always fire a change event when the user interacts with the knob @amuino