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/lib.rs

@@ -0,0 +1,18 @@
+use proc_macro::{self, TokenStream};
+use syn::parse_macro_input;
+
+mod expr;
+
+use expr::{bool_expr_impl, num_expr_impl};
+
+#[proc_macro_derive(BoolExpr)]
+pub fn bool_expr(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input);
+    bool_expr_impl(input)
+}
+
+#[proc_macro_derive(NumExpr)]
+pub fn num_expr(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input);
+    num_expr_impl(input)
+}