BugFixes

• Refactor paging #22:

  • "next" is renamed "advance_page" and "next" returns only 1 element (Python 2 expected behavior)
  • paging objects are now real generator and support the "next()" built-in function without need for "iter()"

• Raise accurate DeserialisationError on incorrect RestAPI discriminator usage #27

• Fix discriminator usage of the base class name #27

• Remove default mutable arguments in Clients #20

• Fix object comparison in some scenarios #24