ddoc: Params for all elements?

[Carlos Santander]

I'm not sure if this should be flagged as a bug, but I find it odd that Params,
Returns, and maybe others are accepted for modules, aliases, classes, and
probably other elements. I mean, what does a module return? What are the
parameters of an alias? I think ddoc shouldn't allow those sections, but I'm not
sure what the exact behavior should be.

And as a related note, whatever is done with the previous issue, should also be 
done when trying to document parameters that don't exist:

/// Params:
/// a = nothing
void foo() {}

-- 
Carlos Santander Bernal