[CHEF-3953] ImmutableMash and ImmutableArray should implement to_hash and to_a respectively
  - ImmutableMash now implements a to_hash method.  This recurses through the ImmutableMash and returns a fully mutable Hash
  - ImmutableArray now implements a to_a method.  This recurses through the ImmutableArray and returns a fully mutable Array
  - Unit tests added for both of the above methods
[CHEF-5132] ImmutableCollections #to_a and #to_hash methods fixed and improved
[CHEF-5132] ImmutableCollections #to_a and #to_hash tests changed to use #be_instance_of and cleaned
[CHEF-5132] more tests added for ImmutableCollections #to_a and #to_hash methods
CHEF-5132: documentation updates