MarathonObject is not hashable in Python3

[jolynch]

From what I can tell MarathonObject et al. are basically record types, but they unfortunately don't have a __hash__ method so in Python3 you can no longer put them in dictionaries or sets, for example:

obj = MarathonObject()
collection[obj] = ...

Works fine on Python 2.7 (because it's using literal identity) but Python3 correctly complains since MarathonObject implements __eq__ but not __hash__.

We pretty frequently put MarathonTasks in sets and such to figure out which tasks are running or not in PaaSTA, so ... either we can refactor PaaSTA to actually have a wrapper type around the types that marathon-python is trying to do, or we can define hash on the MarathonObject class.

I think the right answer is that marathon-python should use a proper record type like namedtuple or something really cool like PRecord. The ok answer would be to just define __hash__ to be the hash of the json representation (which is meh because the object can be mutated so the hash could change which is bad).

I don't want to unilaterally add a dependency on pyrsistent, but I really think that a proper record type instead of hand rolled object hierarchies would be much better.