Fix live editor examples on home page.

Remember that one time I wrote release notes and said:

> This is a breaking change - if you were using class, you must change
> this to className or your components will be visually broken.

Good thing I didn't listen to myself!
Make SelectEventPlugin not throw for range inputs

Accessing .selectionStart on a non-text input will throw (see http://www.w3.org/TR/2009/WD-html5-20090423/editing.html#textFieldSelection), so check that the input has selection capabilities before accessing the property.

Fixes #437.
Merge pull request #438 from spicyj/select-range

Make SelectEventPlugin not throw for range inputs
Use Default Value for Undefined Props

Currently, default props as defined by `getDefaultProps` are only used if a prop is not specified (using `X in Y` check).

However, this makes it difficult for composing components to pass along the state of not being defined, for example:

  render: function() {
    // If `this.props.someProp` is not set, `InnerThing` should use the default value.
    return <InnerThing someProp={this.props.someProp} />;
  }

This changes the requirement for falling back to the default value to an undefined check (using `typeof X === 'undefined'`).
Add clickable anchors to docs headers

Closes #434
docs: remove OUTLINE
docs: Delete Mutation Events (onCharacterDOMModified)
New marketing copy
Don't reset mouseDown in focus handlers

Focus fires after mouse down on initial click, so we lost the
flag when the user initially began dragging on the input.
Changes based on feedback
fixed %d in invariant call
ReactTransitionGroup example: fix typo and logic bug in handleRemove
Fix ReactTransitionEvents detectEvents
Merge pull request #446 from brianr/master

ReactTransitionGroup example: fix typo and logic bug in handleRemove
Update API docs for unmountAndReleaseReactRootNode
typo
Move heading anchors 50px up to avoid nav bar

Fixes #447.

We do this by moving the actual anchored element up in the page without moving the actual text. (Apple uses a similar trick in their framed docs.) Now this looks a bit sillier on smaller screens but it's better overall.
Fix unmounting components mounted into doc element

If we are to unmount a component mounted into a document element we should
unmount it from document.documentElement and not from document.firstChild which
is a doctype element in this specific case.
Merge pull request #423 from andreypopp/master

Re-rendering components into a document leaks components
Make 'disabled' MUST_USE_ATTRIBUTE for compatibility with CSS [disabled] selectors.

When a ReactDOMComponent is created with the property `disabled: true` subsequently setting the property to `disabled: false` the HTML attribute `disabled="true"` was being left in the DOM.