Add new onInput event

'input' is supported in IE9+ and all other browsers according to
https://developer.mozilla.org/en-US/docs/Web/API/window.oninput

Test Plan:
Modified ballmer-peak example to use onInput instead of onKeyUp and
tested that it works properly on latest Chrome.
Update examples to use onInput instead of onKeyUp

onInput has the advantage that it responds to repeated key events before
onKeyUp and is called when modifying the input without the keyboard
(such as pasting with the mouse).

Test Plan:
Opened the ballmer-peak example and docs homepage in Chrome and checked
that both examples update whenever the text is changed.
Simulate input event instead of relying on native

Test Plan:
With the ballmer-peak example (modified to use input), tested that the
percentage updates when adding or deleting text in the field on Chrome
and IE9. After adding es5-shim and es5-sham to the ballmer-peak page,
IE8 works properly too.
Revert "Simulate input event" for now

This reverts commit 580e8f0dbbbb7963c27fee42fd843c6d2a89e2ca.
Merge pull request #32 from spicyj/input

Add new onInput event