Restrict msg_ttl to create and purge key-value operation#834

caspervonb wants to merge 2 commits intomainnats-io/nats.py:mainfrom

ttl-should-only-be-allowed-on-create-and-purgenats-io/nats.py:ttl-should-only-be-allowed-on-create-and-purgeCopy head branch name to clipboard