Add support for <dialog> tag.

fixes #2017
Throw an error when functions on `statics` clash due to duplicate keys
More informative error message for mergeObjectsWithNoDuplicateKeys
Abbreviated error message
Throw if a reserved property is defined in 'statics'
Deprecate 'return false' in event handlers
Re-add  with warning and monitorCodeUse
Fixed style and comment nits
Test for both true and false
More info in monitorCodeUse call
Look on __reactBoundContext for displayName
Add 2048-react to open-source demos

Nothing too complicated, but I think it could be a fun beginner demo.
Update Object.assign polyfill

The spec changed to allow null & undefined sources without throwing.
Now our code depends on this new behavior. The only browser that
implements Object.assign has also updated its native implementation to
this behavior (Firefox Nightly).
Make `npm run-script jest` available

This is slightly shorter than typing `./node_modules/.bin/jest`.
Add example to if else in JSX.
Merge pull request #2076 from whatasunnyday/master

Add example to if else in JSX.
[RFC] Use `accumulateInto` to save even more allocation

Trying to make the event a bit more performant for events.

Feel free to reject this because the API inevitably isn't great. It's good for perf though, and since we're only using `accumulate` in very restrained places, I think we're fine.

`accumulateInto` is `accumulate` that mutates more and allocates less. I kept `accumulate` in case we want that in the future.
Merge pull request #2054 from chenglou/accum

[RFC] Use `accumulateInto` to save even more allocation
Merge pull request #2037 from crm416/duplicate-key

More informative error message for mergeObjectsWithNoDuplicateKeys
Indentation for eventHandlerName