doughlang: Expressions in patterns

ast:
- Document operators
- Parameterize Pat with Annotation
- Consolidate Path and Lit into "Value" (Expr)
- Consolidate NamedRecord/Namedtuple into PatOp::TypePrefixed
- Allow Pat<Pat,*> patterns
- Additional helper functions on Expr and Pat

lexer:
- Support inner-doc comment syntax `//!`
  - Cleans up `///` or `//!` prefix

parser:
- Make Parse::Prec `Default`
- Allow expression elision after `..`/`..=`
- Fix Parser::consume not updating elide_do state
- Add token splitting, to make `&&Expr` and `&&Pat` easier
- error: Embed Pat precedence in ParseError

examples/7fold.rs

@@ -130,7 +130,7 @@ impl<'a> Visit<'a> for CountNodes {
         item.children(self)
     }
 
-    fn visit_pat(&mut self, item: &'a Pat) -> Result<(), Self::Error> {
+    fn visit_pat<A: Annotation>(&mut self, item: &'a Pat<A>) -> Result<(), Self::Error> {
         self.patterns += 1;
         item.children(self)
     }