rfc822header: detect and annotate addresses

rfc822header: detect and annotate addresses

A "list" is a list of addresses,  find them (between the commas) and add
attributes so their rendering can be controlled.
Each address is associated with length, a tag, and the header type.
The tag can be used to look up the actually address in a pane attribute.

Signed-off-by: NeilBrown <neil@brown.name>