fixing issue #25

This makes multiple viewcontroller classes possible in
TLCollectionViewController.

Changes:

- Fix implementation of viewControllerForCell to get correct indexPath during cellFor*AtIndexPath
- update View Controller Backed example
Update pod spec to 0.3.1
Fix for typo in TLIndexPathSectionInfo.m
Merge pull request #27 from kozlek/master

Fix for typo in TLIndexPathSectionInfo.m
Update podspec
Fix podspec