Updating readme to have example of UIBarButtonItem

I'm a complete idiot and spent WAYYYY too long messing with UIBarButtonItem before I realized it took a block parameter.  
Updating README to save someone else the time.
add NSString#cache
Easy to get NSSet from Array and also reverse.
fix with enumerable methods.
NSURL -> NSData
Merge pull request #56 from matsu911/master

implemented NSURL -> NSData conversion method
Merge pull request #54 from katsuyoshi/nested_anonymous

fix with enumerable methods.
Merge pull request #53 from katsuyoshi/array_set

Easy to get NSSet from Array and also reverse.
Merge pull request #52 from katsuyoshi/cache_dir

add NSString#cache
Merge pull request #51 from GantMan/master

Adding Example to README
update README timer examples
this call to didMoveToParentViewController is not needed (gets called twice, that's no good)
spec for nsurl.nsdata method
Adding pop method to UIViewController with tests
Merge remote-tracking branch 'upstream/master'
Merge pull request #57 from GantMan/master

Adding pop to UIViewController
some more date formats
version bump
fix for trying to pop off too many controllers
extend NSString#exists? to the outside of document