Add examples on how to send messages to rooms

This adds two similar examples, one using matrix.client, and the other using
matrix.api.

examples/client-send-message.lua

@@ -0,0 +1,24 @@
+#! /usr/bin/env lua
+--
+-- send-message.lua
+-- Copyright (C) 2016 Adrian Perez <aperez@igalia.com>
+--
+-- Distributed under terms of the MIT license.
+--
+
+if #arg ~= 4 then
+   io.stderr:write(string.format("Usage: %s <homeserver-URL> <username> <password> <room>\n", arg[0]))
+   os.exit(1)
+end
+
+local client = require "matrix" .client(arg[1])
+client:login_with_password(arg[2], arg[3])
+
+-- FIXME: This does not resolve room aliases, it works only with room IDs
+local room = client.rooms[arg[4]]
+if not room then
+   room = client:join_room(arg[4])
+end
+
+room:send_text(io.read("*a"))
+client:logout()