Linked view controllers can now optionally use top/bottom layout guides.

Fixes issue #14.
RBStoryboardLinkSource.h should be a public header

Exposing RBStoryboardLinkSource.h as a public header.
Merge pull request #15 from cmittendorf/patch-1

RBStoryboardLinkSource.h should be a public header
Updated podspec for new tag.
Merge from upstream

Conflicts:
	LinkedStoryboards/Podfile.lock
	RBStoryboardLink.m
	RBStoryboardLink.podspec