Minor fix to avoid crashing when there is no section header.
Merge branch 'master' of github.com:boherna/CHTCollectionViewWaterfallLayout

# By Nelson Tai (4) and Andreas Maechler (2)
# Via Nelson Tai
* 'master' of github.com:boherna/CHTCollectionViewWaterfallLayout:
  Update podspec and README
  Change some properties and methods to imitate UICollectionViewFlowLayout's usage as much as possible - Don't need to calculate item size by yourself. - Also fix some issues with frame calculation.
  Call [super initWithCoder] instead of init
  Section header and/or footer should work properly
  Call [self commonInit] also in initWithCoder:
  [Fix] shouldInvalidateLayoutForBoundsChange

Conflicts:
	CHTCollectionViewWaterfallLayout.m