All channels are now marked as either being bind channels or non-bind channels
with specific markers for CHILD and INTERNAL bind channels.

This will be useful for the next stage, which is enabling region threads to
query the type of channel that they are trying to create endpoint context for.

* New enum: fplainn::Channel::bindChannelTypeE.
  ^ States whether or not a channel is a bind channel.
  ^ In addition, also gives what type of bind channel it is, if it is one.