Illustrate scroll view problem.
Add new `floating` (BOOL) property.

This property allows the NoticeView to be floating at the same position
in a UIScrollView, while the user is scrolling. It's pretty much the
same implementation as in the pull request #41, using KVO. It's just
based upon the most recent HEAD of master, and includes some fix
(leaked observers). There're also two new buttons in the example project
to test it.
Merge pull request #43 from plu/master

Add new `floating` (BOOL) property. (KVO + UIScrollView solution)