Support deprecated in option pragmas

[arnetheduck]

Sometimes a flag is removed from the UX after being made obsolete - similar to hidden, it should be possible to mark an option deprecated so that it's still parsed, but allowing the code to use the deprecation features of the language and potentially notify the user that the flag will no longer parse correctly in future releases.

See https://github.com/status-im/nimbus-eth2/blob/aff0505807ed81d7ca1677117dcfa9b30707eb50/beacon_chain/nimbus_beacon_node.nim#L1775 for examples.