Add serialization support for heapless v0.8 and v0.9#295

mandrean wants to merge 1 commit intojamesmunns:mainjamesmunns/postcard:mainfrom

mandrean:fix/heapless-v08-v09-serializationmandrean/postcard:fix/heapless-v08-v09-serializationCopy head branch name to clipboard