Ensure that Ports that do and don't use type metadata can be relayed to each other, or cause an error

[colinbdclark]

It appears that if you have two Ports, one of which uses argument type metadata (with the metadata: true option), and the other does not, they will fail to properly relay to each other using osc.Relay. As reported in #185, an error occurs deep within the process of writing messages. This appears to also be the case when relaying in raw: true mode, which is very strange.