Add new methods to objects, collections and dictionaries

* tap - Calls the function with the object, and then returns object
* pick - Returns a new dictionary only with choosen keys
* omit - Returns a new dictionary without omited keys
* merge - Returns a new Dictionary with merged values
* keys - Returns an array instead of MapCollectionView
* values - Returns an array instead of MapCollectionView
Update README with new functions
Fix .xcodeproj adding CarExample
Change .merge to accept variable number of arguments
Merge pull request #10 from bastos/add-new-functions

Add new methods to objects, collections and dictionaries