Optionals cause 1 bool + size of orignal type. Due to alignment needs, this can balloon to 8 bytes for 64-bit integers. Making an optional 8 byte integer take 16 bytes.

• Add support for Markable in IDL. See https://github.com/akrzemi1/markable
• Add a new value for fields called marked_value to indicate which value it should use as the sentinel value.
• Add support for bool, enum and int types
• Switch optional bools
• Add support for types like OpTime and BSONObj potentially