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.
Merge pull request #18 from bjhomer/pull-requests/token-field-text-did-change

Add a delegate method to notify when the text field text has changed.
Merge pull request #19 from bjhomer/pull-requests/align-tokens-vertically-with-text-field

Align tokens on the last line vertically with the text field.
Add API for removing all tokens.
Merge pull request #20 from bjhomer/pull-requests/remove-all-tokens

Add API for removing all tokens.
Add delegate method to disallow deleting tokens.
Don't animate the frame around if the view isn't on screen yet.

This was causing a problem when the token field was in a view that
was presented modally. `layoutSubviews` was called after the view
was added to the window, but before it had any original frame. Thus,
the animateWithDuration call here was causing it to animate from
CGRectZero, which looked odd.
Merge pull request #23 from bjhomer/pull-requests/should-remove

Add delegate method to disallow deleting tokens.
Merge pull request #24 from bjhomer/pull-requests/dont-animate-when-not-visible

Don't animate the frame around if the view isn't on screen yet.
Improve how token field handle Backspace and highligh token

Highlight token only when text field has NO text and user press backward (rather than the text field have ONE character and user press backward)
Check respondsToSelector before calling an @optional delegate method.

Oops.
Merge pull request #26 from bjhomer/pull-requests/behavior-fixes

Bug fixes.
Make Xcode 4.6-recommended changes to pbxproj.
Merge pull request #29 from bjhomer/pull-requests/xcode46

Make Xcode 4.6-recommended changes to pbxproj.
Update README.mdown
Update README.mdown
Fixed warning when checking if delegate implements callback

Signed-off-by: Jai Govindani <jai@monstermedia.co.th>