Sends a smaller available height to footers if content view is less than total frame height

Otherwise, behaves as normal, sending max float
Merge branch 'master' of github.com:carsonb/PSCollectionView into feature/incremental-insertion-deletion

Conflicts:
	PSCollectionView.m
Merge branch 'feature/incremental-insertion-deletion' of github.com:carsonb/PSCollectionView into feature/sections