Fixes for pull request, tidying up method signatures

also use of firstObject for safer lookup of error messages
Adding category on Dictionary for null values
Update README.md
Merge branch 'refs/heads/master' into add_carpool_functionality

Conflicts:
	README.md
Updated cocoapods gem version
Merge pull request #7 from snowpool/add_carpool_functionality

Add carpool functionality
Merge branch 'master' into builder_method

Conflicts:
	Snowpool/Controllers/SPLAddCarpoolViewController.m