A new preprocess method is added to the template engine in order to do
preprocessing/sanitization of the templates before compilation.
This method can be overloaded in order to add new features such as
translation, ...
* 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)
Christophe Matthieu