Stream improvements, custom command improvements, and more

The major feature of this release is improvements to the
CadenceBot-forwarded CadenceRadio stream.

This update introduces configurable options to the stream - An
administrator may now configure stream volume and the number of retries
made when a stream packet is dropped, in addition to the bitrate. Additionally, the stream is now a broadcast - Instead of getting a new connection to Cadence for each Discord server that wants to listen, CadenceBot now broadcasts a single stream to all listeners. This is much nicer for network consumption.

This update also introduces the "multitargeted" type of custom command.
These are allowed to include multiple words which can be formatted into
the response.

Minor improvements include adding 'maillog', which can trigger the
maillog script when the command is run in the server - this is disabled
by default and intended for debugging, improvements for the mechanics of
targeted custom commands, and timezoned logging.