The props validation code is actually quite difficult to get right.
Also, it is sometimes useful to be able to validate an object against a
specified schema. Therefore, this commit exports the standalone validate
function as an utility function.
including:
- add a link to the tutorial in the main readme page
- remove learning page on 'env', move content on reference page
- add dynamic sub components section in component page
- add reference page on props
- split qweb page into engine/language pages
- move t-key information into qweb language page