add support for vertical spacing in grid layout
update the demo to show vertical spacing in grid
Merge pull request #113 from jwilling/grid-vertical-spacing

Grid vertical spacing
Fix issue preventing display of supplementary views when registered from a nib

When a supplementary view is registered via -[JNWCollectionView registerNib:forSupplementaryViewOfKind:withReuseIdentifier:], the collection view would never display it.

The cause was that supplementaryViewNibMap was never including when searching for supplementary view identifiers.
Merge pull request #116 from nerdyc/supplementary-nibs-fix

Fix issue preventing display of supplementary views when registered from...
Add collectionView:didRemoveCell:forItemAtIndexPath: message to JNWCollectionViewDelegate protocol
Wrap comment
Rename message to collectionView:didEndDisplayingCell:forItemAtIndexPath:
Use property accesor instead of ivar
Merge pull request #118 from plumbojumbo/delegate-didremovecell

Add collectionView:didRemoveCell:forItemAtIndexPath: message to JNWCollectionViewDelegate
Merge remote-tracking branch 'upstream/master'