A few minor improvements to the demo.
Explode animation controller snapshot performance improved

The explode animation now takes an initial snapshot before taking the snapshots for each of the exploding sections. On device testing shows that this reduces the total snapshot time from ~1050ms down to ~60ms

Fixes #7
Ensure that interactive transitions are never 100% completed

With is a workaround for #4
Add NatGeo-inspited transition
Add screenshots for NatGeo transition, update docs.
Change NatGeo screenshots to 4".
Modified to use keyframe animation

Also the completion block now passed the cancellation from the transition context.
ipad shares iphone storyboard
Merge pull request #11 from xinsight/add/ipad-fix

ipad uses iphone storyboard
natgeo: fix rounding errors
do not rely on container view frame values, rm hardcoded screensize
Minor tidyup

Removed a comment which relates to the bug fix rather than the intent. Replaced a CGRectMake with a CGRectOffset - I find this easier to read!
Merge pull request #13 from xinsight/fix/rounding

natgeo: fix rounding errors
Fix to CEHorizontalSwipeInteractionController when UIPanGestureRecognizer translation.x == 0

Sometimes handleGesture: incorrectly sets the BOOL rightToLeftSwipe to
false when it should be true…This is due to [gestureRecognizer
translationInView:gestureRecognizer.view.superview] sporadically
returning {0, 0}; usually this occurs when making slow, methodical
movement swipes while starting at center of view window.  Solution is
to break anytime {0, 0} is returned (where translation.x == 0) so that
nothing happens.
Added a few comments
Added portal animation from ZEN BabyBook app

Kindly contributed by FreddyF. Original source here:
https://github.com/FredddyF/BabyBook-v2--iOS7-/blob/master/ZEN%20BabyBook/ZENPortalAnimationController.m
Renamed portal animation adding the 'CE' prefix
Portal animation reverses properly

A few minor changes:
 + The forward animation uses snapshots. These have to be replaced with the real views when the animation completes
 + The reverse animation snapshots a view which hasn't been added to the hierarchy. This needs to be added in order to snapshot properly (you get unexpected behaviour otherwise)
Added documentation for portal animation