Support conditional queries

[ekryski]

Conditionals we should support:

• $in
• $or
• $nin
• $not

By default all queries are and queries so that isn't required.

I don't think we need to support complex conditional queries, at least not off the bat, but simple ones should work the same as when using feathers-mongo and feathers-mongoose.

Let's take a todo list example and say I want to get todos that were created on or after a certain date and only if they have a "complete" or "incomplete" status. When sending a GET request to /todos, the non-encoded url params might look like this:

{
  date: {
    $gte: "2015-10-25T18:13:12.843Z"
  },
  $or: [
    { "status": "complete" },
    { "status": "incomplete" }
  ]
}