Adding in the ability to easily create queries in the format used by MongoDBs console

The question "How do I pass json style queries in to the C# driver" pops up on Stackoverflow quite often. This seems like a reasonably elegant way to add it (perhaps we could look into creating a specific call, to improve error handling for when people get the query wrong though)

e.g. 
http://stackoverflow.com/questions/17220959/c-sharp-mongo-queries-with-json-strings/17221345
http://stackoverflow.com/questions/6120629/can-i-do-a-text-query-with-the-mongodb-c-sharp-driver

Usage:
collection.Find(new JSQueryDocument("{ SendId: 4, 'Events.Code' : { $all : [2], $nin : [3] } }"));

I also ended up writing wrappers around all the MongoCollection methods that take in IQueryDocuments so that you can just provide strings instead - e.g.

collection.Find("{ SendId: 4, 'Events.Code' : { $all : [2], $nin : [3] } }");

See comments below as to why we went with that signature