Tagged messages

[kpcyrd]

Especially since binary support was introduced, it might be needed to tag messages and filter messages by tags when printing them.

The interface would be along the lines of:

tr1pctl write -t foo
tr1pctl ls -t foo

Internally, this would need a breaking change in the file format to introduce . Since the tag is optional, this would map to an Option<T>, with None being a length of 0. If the tag is exposed as Vec<u8> or String still needs to be decided.