Initial support for MongoDB.

Support simple queries using the a JSON format:
{
	"collection" : THE NAME OF THE COLLECTION TO QUERY,
	"query" : {
		A DICTIONARY FOR QUERYING FIELDS (similar to what you would find in PyMongo
	},
	"fields" : {
		LIST OF FIELDS TO RETURN IN THE SPECIFIED ORDER
	},
	"sort" : {
		LIST OF FIELDS TO SORT BY (1 - Ascending, -1 - descending)
	}
}

For example:
{
	"collection" : "mycoolcollection",
	"query" : {
		"fieldA" : { "$gte" : 5 },
		"created" : { "$lt" : "ISODate(\"2014-09-01 23:43\")" }
	},
	"fields" : {
		"fieldA" : 1,
		"created" : 2
	},
	"sort" : {
		"created" : -1
	}
}
removed a debug message and change to a better error message when collection is not specified.
added extra error handling for invalid query and invalid database name
Merge pull request #298 from erans/master

Initial support for MongoDB.