3.0 Query builder part 2

I've added a few more sections to the query builder docs. The usage for `insert()`, `update()` and `delete()` is a bit awkward, but I've made cakephp/cakephp#2550 to remind us to fix/improve it.

The cached query example using listeners is also a bit awkward, it is making me think we might want to add a simple way to do cached results onto the ORM\Query class. While doing so might introduce some coupling between the ORM + caching package it will make an easier to use API for developers. I'll probably open a separate issue with a proposal.