rm make_exprs.py, moving to the c part

- add src/expr.zig

src/expr.zig

@@ -0,0 +1,28 @@
+const Token = @import("token.zig").Token;
+
+pub const Binary = struct {
+    left: Expr,
+    operator: Token,
+    right: Expr,
+};
+
+pub const Grouping = struct {
+    expression: Expr,
+};
+
+pub const Unary = struct {
+    operator: Token,
+    right: Expr,
+};
+
+pub const ExprType = enum {
+    Binary,
+    Grouping,
+    Unary,
+};
+
+pub const Expr = union(ExprType) {
+    Binary: Binary,
+    Grouping: Grouping,
+    Unary: Unary,
+};