various documentation additions and refactors for operations module
various documentation additions and refactors for operations module

saghm/mongo-rust-driver-prototype,r-arias/mongo-rust-driver-prototype,saghm/mongo-rust-driver-prototype,mongodbinc-interns/mongo-rust-driver-prototype,kyeah/mongo-rust-driver-prototype,mongodb-labs/mongo-rust-driver-prototype,mongodb-labs/mongo-rust-driver-prototype,DenisKolodin/mongo-rust-driver-prototype