Ensure to add child controls of container controls added after the windows is opened. Fixes #60.
Ensuring that checking and unchecking methods of the Checkbox control work. Fixing #61.
Correcting code style in Checkbox class. Incorrect usage of the bang operator. Breaking change!
Allow multiple items to be selected in multi-select listboxes. Fixes #62.
Listbox size and multiple argument sanitizing. Fixes #64, #66
Adding events for when Window recevied and looses focus.

Not tested in OSX.

Fixes #68.
Merge branch 'master' of https://github.com/thomthom/SKUI
Merge remote-tracking branch 'tt/master'