Added some missing packets

I have found a relatively old thread on darkblizz.org (August 6th, 2010) which seems to have stemmed from this thread on vL by Hdx, which outlined some packets that our documentation was missing.

As such, I have added these packets to our documentation:

• S>C 0x17 SID_READMEMORY
• C>S 0x17 SID_READMEMORY
• S>C 0x20 SID_ANNOUNCEMENT
• S>C 0x23 SID_WRITECOOKIE
• S>C 0x24 SID_READCOOKIE
• C>S 0x24 SID_READCOOKIE
• S>C 0x43 SID_WARCRAFTUNKNOWN