Implement NAMES command

[progval]

It should be a simple matter of re-using this code in lib/irc/handler.ex:

matrix2051/lib/matrix_client/poller.ex

Lines 1083 to 1106 in e1b664a

	# send RPL_NAMREPLY
	overhead = make_numeric.("353", ["=", channel, ""]) |> M51.Irc.Command.format() |> byte_size()
	# note for later: if we ever implement prefixes, make sure to add them
	# *after* calling nick2nuh; we don't want to have prefixes in the username part.
	M51.MatrixClient.State.room_members(state, room_id)
	|> Enum.map(fn {user_id, _member} ->
	nuh = nick2nuh(user_id)
	# M51.Irc.Command does not escape " " in trailing
	String.replace(nuh, " ", "\\s") <> " "
	end)
	|> Enum.sort()
	|> M51.Irc.WordWrap.join_tokens(512 - overhead)
	|> Enum.map(fn line ->
	line = line |> String.trim_trailing()
	if line != "" do
	# RPL_NAMREPLY
	send_numeric.("353", ["=", channel, line])
	end
	end)
	# RPL_ENDOFNAMES
	send_numeric.("366", [channel, "End of /NAMES list"])

Suggested by @Thaodan in #14 (comment)