Documentation

[thinker227]

Allow doc comments above variables and functions which are available on the node and symbol as well as displayed in Intellisense. Doc comments should likely start with /// and can contain simple markdown.

/// This is a doc comment for `x`. 
let x = 0;

/// This is a doc comment for `f`. 
/// It always returns [`x`]. 
func f() => x;

For a non-hacky implementation, a concrete syntax tree (#29) would be quite useful before implementing this. This could already be implemented though since some tokens exist in the AST, and doc comments should only be able to appear on eg. let and func tokens. Still need whitespace in tokens though.