class library: translations between key value pairs, asscociations, and dictionaries

This solution was suggested in the discussion about inject and it fixes #1245. The additional methods provides convenient transition between three commonly used and useful data structures:

key value pairs: common representation of arguments
collections of associations: ordering, array and collection methods
dictionaries: fast lookup, event compatibility

A possible improvement could be a primitive for the hasAssociations method, which currently prone to be misunderstood (too inefficient would have been the other choice).