conlang: Add constructor expression for structs!

grammar:
- Add new rules `PathLike`, `Structor`, `Fielder`
- Replace Path with PathLike in Primary expressions

cl-ast:
- Add nodes for Structor and Fielder

cl-parser:
- Add branch to path-expression parsing
- Parse Structor bodies

interpret:
- Add TODO

compiler/cl-parser/src/error.rs

@@ -91,6 +91,8 @@ pub enum Parsing {
     Unary,
     UnaryKind,
     Index,
+    Structor,
+    Fielder,
     Call,
     Member,
     PathExpr,
@@ -190,6 +192,8 @@ impl Display for Parsing {
             Parsing::Unary => "a unary expression",
             Parsing::UnaryKind => "a unary operator",
             Parsing::Index => "an indexing expression",
+            Parsing::Structor => "a struct constructor expression",
+            Parsing::Fielder => "a struct field expression",
             Parsing::Call => "a call expression",
             Parsing::Member => "a member access expression",
             Parsing::PathExpr => "a path",