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.
Consistently use autoBind on homepage examples

Except for todo.js, all the other examples on the homepage use React.autoBind
when defining event handler methods.

Test Plan: Added todo items successfully
Add JSFiddle to the getting started section
Add why-react
[docs] Add RSS feed.xml for blog posts

uses `feed.xml` from https://github.com/snaptortoise/jekyll-rss-feeds
(slightly modified for `site.url` + `site.baseurl`)
@vjeux @benjamn
Break lines
[docs] Use date_to_xmlschema in feed.xml
[docs] RSS: Pass title through xml_escape
@jeffreylin
Merge pull request #48 from petehunt/add-blog

Add "Why React"
Highlight additional change in tutorial12.js

tutorial12.js switches from using this.props to this.state. Let's highlight the change on line 10 as well to make that clear.
Merge pull request #51 from dschafer/patch-1

Highlight additional change in tutorial12.js
Merge pull request #41 from divad12/homepage-examples-autobind

Consistently use autoBind on homepage examples
Improve blog setup

* All posts under blog/
* Index @ blog/index.html
* Only show excerpt on index with "continue reading" link
* Date, name formatting improvements (better for humans)

It could probably still use some style tweaks but I feel better about
it.

Moving forward, we'll use the "excerpt" feature of Jekyll with the
default separator, which is just 2 newlines. So the first paragraph will
be special. Alternatively you can specify excerpt, but we'll want to fix
the layout so that gets added in.
Merge pull request #52 from zpao/blog-tweaks

Improve blog setup
Merge pull request #49 from paulshen/jekyllrss

[docs] Add RSS feed.xml for blog posts
Merge pull request #43 from vjeux/jsfiddle

Add JSFiddle to the getting started section