Introduction tutorial

Suggestion for making a start on the tutorials. This is probably not complete (I shall probably remember things I've forgotten five minutes after submitting), but it can serve as a starting point.

I think tutorials should supplement what's in the api docs and examples, providing more detailed info on specific subjects. I would like to see more detailed tutorials on:
* event handling
* rendering process
* projection handling
* custom building

I can make a start on these, but I'm not an expert on the first two, so others would have to expand.

Not sure it's a good idea having these tutorials as hbs; not easy to read on Github.