* Improve messages.inc and message_stocks.inc documentation
* Fix typos
* Fixed typos, added a bunch of @notes and better register_message callback function explanation
* Removed extra argument in set_msg_arg_string
* Creates => Sends
1) Moved message_begin, message_end, and write_ natives to messages.inc
2) Moved MSG constants to message_const.inc
All completely backwards compatible with compiling older plugins of course :)