add docs to mem.go functions
add docs to mem.go functions

tpukep/caps,zombiezen/go-capnproto2,hodduc/go-capnproto2,hodduc/go-capnproto2,zombiezen/go-capnproto,jmckaskill/go-capnproto,zombiezen/go-capnproto,zombiezen/go-capnproto2