Add random word util.
Move Opts placement into Bot, reference in Sess.
recvq interface and thread pool mgmt related improvements.
Disambiguate Socket::ep initializer lambda return type.
Minor cleanup.
Use steady_timer convenience typedef.
Add preliminary HTTP message handler. Renames proxy option key.
Change logging format.
Add Sess state flags.
Fix some possible race conditions.
Add sendq purge for a terminating instance; related cleanup.
Clean/move some session negotiation logic into Bot.
Rename FlushHold/hold.
Callback mapping for sendq socket errors.
Split Cork.
Additional event handler caller overloads.
Add session states, state changes, and minor handler reorg.
Recvq will continue unless true interrupt.
Rename Flag to Flags.
Fix and improve sendq related.
Minor cleanup; formatting, ctors.