Specs for custom save/create methods
Implement Model.method_for; specs pass.
Move default method actions into model.rb
Use primary_key_field in forming association paths
Remove .primary_key_field class method

Now this code follows the same pattern as other Her configuration
class methods, where a nil argument means you want to return the
existing value (not set a new value).
Merge branch 'custom-rest-methods'

Conflicts:
	lib/her/model.rb
	lib/her/model/orm.rb