feat!(core): Use new AST structure

Derive Expr methods using a derive proc-macro. These macros are present in
the `argus-derive` crate, but the traits are defined in `argus-core`

argus-derive/src/expr.rs

@@ -0,0 +1,5 @@
+mod bool_expr;
+mod num_expr;
+
+pub use bool_expr::*;
+pub use num_expr::*;