Just finished making an example AI mod for anyone interested in writing their own - called it MicroAI*
*because it's small, it doesn't do micro for you.
It's about 350 lines of lua in total, and is downloadable from the vault or GitHub: https://github.com/HardlySoftly/MicroAI
In terms of how good it is, I'd place it above Normal AI and below Adaptive AI.
If people have questions about it or AI modding in general I'm happy to take them in the replies