Added a voice announcement system for the AI. [CHANGELOG]

* Voices are based on /vg/'s female voice and are copyright free.
* There is a 60 second cooldown for each announcement.
* Added a compile option for AI voices. Undefining AI_VOX will not compile the voice resources, meaning players won't have to download them.

http://youtu.be/ggmIFiAMY5U