Version 2.2

Fix possible crash.

Version 2.1

Swift 3 support.

Version 2.0

Update UICollectionView's empty data set after performBatchUpdates.

Version 1.9

Fix memory leak.

Version 1.8

Optimize custom empty data view layout.

Version 1.7

Add function updateEmptyDataSetIfNeeded() to force update emptyDataSet.

Version 1.6

Support multiple vertical spaces.

Version 1.5

Fix content view frame issue when empty data view is custom.

Version 1.4

1. Support Swift 2.2.
2. Fix the bug "header view or section header been hidden by emptyDataSet".

Version 1.3

Support CocoaPods now.