Observe state with delegate

[0xch4z]

Thanks for the library! It would be cool if there was a delegate protocol to preform actions on the drawer state changing rather than having to pass a completion handler in. For example, the following stubs:

func drawerController?(willOpenSide side: DrawerSide)

func drawerController?(willCloseSide side: DrawerSide)

I'd be happy to submit a PR.

Thanks,
Charles

[kawoou]

Sounds like a good idea😆
Do I add this? Or if you would like to upload your own PR, I'll be happy to review.

[0xch4z]

Sweet, thanks. Just added PR #16. Already using this in my own project and it's a big help for changing the status bar color when the drawer is open.

Let me know if I need to change anything!