Raw API documentation is not sufficient for people to learn the working
principles of the API, especially when they already know the old one. And some
things have changed since the opendays so the presentations don't reflect the
current state of affairs.
Closes#3483
* document qweb based (mostly) on JS version
* convert JS qweb tests to (mostly) language-independent XML so they can be
used for JS and Python implementations
* add some more tests (e.g. precedence between t-value and body in t-set)
* remove ``t-import``
* fix parity in foreach(dict) (and rename some variables to make array and
object versions more similar)
Max Hellwig
Xavier Morel
Raphael Collet