Omits the updater since 1) they're not as obviously useful as setters are, 2) they don't work if a field's replacement value is computed from multiple fields of the record, and 3) the code they encapsulate is easy to write with setters
Only provides the definition form define-record-setter, not the expression form record-set since it's not obvious whether that should be a macro which accepts the static record info (and thus has a bit of a code size expansion problem) or if it should be a function that accepts the dynamic record descriptor
Closes #185, but with API changes:
define-record-setter, not the expression formrecord-setsince it's not obvious whether that should be a macro which accepts the static record info (and thus has a bit of a code size expansion problem) or if it should be a function that accepts the dynamic record descriptor