consolidate deserialization routines

[ralexstokes]

#81 consolidated the serialization routines, with a major benefit of letting the ser code in the proc macro call out to the one set of routines in the main library

let's do a similar refactor for deserialization

I'd say this is a "good first issue" if you just mirror the approach in #81 for serialization code

[ralexstokes]

after some thought, this doesn't seem to pull its weight as it would mainly just save the extra deserialization maintenance for containers -- happy to entertain a PR here if someone sees this in the future and thinks it would add value