Fix double-binding to submit event

Fixes #916.
Change LinkedValueMixin to a util class

This makes it clear that .getValue() is not a public API.
Merge pull request #748 from spicyj/private-getvalue

Change LinkedValueMixin to a util class
Implement stricter whitespace rules
Update broken link in 'why react' article
Normalize internal links in 'why react' article
Support two-way binding for checkboxes in LinkedValueMixin via 'checkedLink' property
Add invariant if both checkedLink and valueLink are provided
Fix typo in ReactDOMInput-test
Fix comparison in _handleLinkedCheckChange
Use Simulate.click instead of Simulate.input for simulating input on
checkbox.
Merge pull request #952 from jeanlauliac/patch-1

Update broken link in 'why react' article
Fix typo
Upgrade Commoner to v0.8.14 for multiple file support.

See [Commoner's README.md](
https://github.com/benjamn/commoner#generating-multiple-files-from-one-source-module)
for further explanation of the new functionality.

Among other potential benefits, this upgrade allows us to generate source
maps as standalone files rather than appending them inline to every
compiled module file under `build/modules/` (see #833).
Merge pull request #480 from syranide/whitespace

JSX whitespace coalescing rules
Merge pull request #959 from benjamn/commoner-multiple-file-support

Upgrade Commoner to v0.8.14 for multiple file support.
Don't reconcile children unneccessarily

We've talked about this perf optimization for a while now. This prevents us from re-reconciling components that are above the component being
reconciled in the owner hierarchy.
Transfer the key prop in cloneWithProps

`cloneWithProps` uses `ReactPropTransferer`, which ignores the `key`
prop. See https://github.com/facebook/react/pull/713

However, this is not the case with `cloneWithProps` because when someone
is cloning a component and provides a key, they mean for the clone to
take it.
Codemod for whitespace change

This codemods to shim any old-style JSX whitespace so that it renders the same as before.
Basically it sticks explicit `{' '}` spaces in where spaces are no longer implicit.
Merge pull request #958 from aymanosman/master

Fix typo