Create project for interactive VC transitions
Completed simple storyboard project which displays a modal controller

Nothing fancy - allows the VC to be displayed and dismissed with buttons.
Create a flip transition to show/dismiss the modal VC

This isn't currently interactive, but when the VC is displayed it will
appear via the vertical flip animation.
This is a WIP. Well, it doesn't work yet. Come back later...
Lots of refactoring

Removed a lot of code. Only the display of the modal VC is interactive
at the moment, but it works pretty well. Will fix the dismissal soon.
Interactive dismissal works now as well

We have to set the target of the interactive transition in each of the
view controller's viewDidAppear methods.
Updates so that we only complete the transition if pan is long enough
Replaces UIView transition with custom animation

There appears to be a bug in the transitions which means that they don't
cancel or complete correctly. Therefore we've reimplemented the same flip
as a custom key-frame animation.
Completed writeup for interactive view controller transitions

Still needs images, and links.
Adds images to the writeup
Updates source files with correct license header
Merge branch 'days/14-interactive-vc-transitions'