Get the label vertical layout more right.
Make the text field hang below the "To:" label like the buttons do.

This supersedes f284a8ee871992d759f184c21072755748b36c31.
Teach JSTokenButton to handle backspace.

This allows removing the _hiddenTextField entirely from
JSTokenField, and automatically enforces highlighting the
currently selected token.
(cherry picked from commit 3273b5b30bfb88f540b4f7550b4a30749f6c3c0d)
Don't modify the array of tokens while we're iterating it.
(cherry picked from commit 7be366b42e8d3bf0f99eb8a8c4e38f5b85331a42)
Detect deletion of invsible space, even if it's not the whole text.
Merge pull request #3 from bjhomer/button-deleteBackward

Teach JSTokenButton to handle backspace.
Merge pull request #4 from bjhomer/layout-fixes

Layout fixes
(manually merging pull request from bjhomer) Don't modify the array of tokens while we're iterating it.
Merge pull request #5 from bjhomer/crash-fix

Don't modify the array of tokens while we're iterating it.
(Manually merging BJHomer's commits: Make the didAdd and didRemove delegate methods consistent, and Allow removing tokens by represented object.
fix method name which passed to respondsToSelector method.
set zero width space string on token add instead of relying on handler
Merge pull request #11 from vishl/master

Fix delete on iOS 6
Merge pull request #10 from hirakiuc/patch-fix-old-delegate-method-name

fix method name which passed to respondsToSelector method.
when add token to the field, add zero width space so that backspace will delete the text
Merge pull request #14 from siuying/delete-fix

Fixes problem adding or removing tokens in iOS 6
Remove ZERO_WIDTH_SPACE_STRING, relying on iOS 6 to do it right.

As of iOS 6, a UITextField subclass will receive -deleteBackward
even when the text field is empty. So ZERO_WIDTH_SPACE_STRING is
no longer needed there.
Add a delegate method to notify when the text field text has changed.

This is simpler than requiring the client to call -addTarget:action:...
on our textField.
Align tokens on the last line vertically with the text field.

If the text field is larger than the JSTokenButton images, the
buttons may appear to float higher than the text, which looks
odd and distracting.

Note that this means that when the text field wraps to a new line,
the previous line's tokens may shift vertically to fit more compactly
with each other, if the text field is taller than the tokens.
Merge pull request #17 from bjhomer/pull-requests/ios-6

Remove ZERO_WIDTH_SPACE_STRING, relying on iOS 6 to do it right.