Deleted general/split-elements (use mx/transpose instead)
revise transmit-utterances into speaker-plus-utterances

guts of transmit-utterances now in make-utterances
Style update replace when with if ... nil to make nil return explicit.
Transmissions now use propn ids rather than indexes

This will be a little less efficient, probably, but makes it a *lot*
easier to investigate at the repl.
Gave persons different max-utterances
transmissions now include speaker
In update-talk-to-persons prevent talking to oneself