Documentation generator

[rprimet]

Odoc/javadoc/... equivalent for Catala.

From a Catala source file containing specific docstrings (e.g. beginning in ## ?), output markdown or html documentation

[AltGr]

On the syntax side: we already support e.g.

#[doc = "this is a documentation attribute"]

(where the string can be multi-line)

it shouldn't be difficult to add ## as syntactic sugar for the above (with some care for multi-line).

The doc generation itself is another story, though ; but it can be worked on in parallel. Retrieving the kind and name of the corresponding decl shouldn't be difficult, and the type information should be readily available in desugared. We should use markdown for the contents.

Then come the problems of formatting. I remember odoc had huge difficulties to properly resolve cross-references... but we probably don't need to get that far yet.