Set the notification window to hidden

By setting the hidden flag, the OS will poll the status bar style of the original view controller. Without this flag, the status bar will always become black after the notification animation.
Merge pull request #22 from epologee/patch-1

Set the notification window to hidden
subclass UIWindow

thanks to @dzenbot for this fix
added note about swift version to read me
Merge commit '7a05a62c163dd8286f703b0cdf8daa898b0355ee'

* commit '7a05a62c163dd8286f703b0cdf8daa898b0355ee':
  added note about swift version to read me
  subclass UIWindow
  Set the notification window to hidden

Conflicts:
	CWStatusBarNotification/CWStatusBarNotification.m