Add tests for Relation queries

Making an Object, and then marking that it's got Relation's doesn't
work. These tests demonstrate that. Next commit will fix whatever's
needed so that these tests pass.
Fix the relatedTo operator in Query

Before this we were never passing in all of the data required for the
relation lookup to work.

Figured this out after looking at the 4th code example at
https://parse.com/docs/rest#queries-relational and comparing to the
request that was actually being sent.

All the tests pass now.
Add a test for Query.filter(foo__in=[list_of_Objects])

It currently fails because:
  TypeError: <Game:XKz5Hfyxqw> is not JSON serializable
Make Query.filter(foo__in=[list_of_Objects]) work

Basically, if we're asked to convert_to_parse a list, do it for
everything in the list and return the list.

All of the tests pass now, so I don't believe anything has been harmed
in this change.
Merge pull request #59 from dgadling/master

Fix the relatedTo Query operator