Fix index creation and query

[TomMD]

Index creation is broken (see #111).

In Mongo 3.6+ we can use the new MSG_OP format. The MSG OP for index creation isn't documented but they indicate the c library is a suitable reference (https://github.com/mongodb/mongo-c-driver/blob/master/src/libmongoc/src/mongoc/mongoc-index.c#L26). Hopefully fixing index creation and query will be simple as declaring a new structure, defining the BSON encoding, defining the MSG_OP Notice and opcode next to the existing Update, Insert, Delete, and KillCursors values, and exposing the high level functions.