Add Rust target

spec/test_custom_lex_fn.rs

@@ -0,0 +1,8 @@
+use testparser::*;
+
+fn main() {
+    let mut c = p_context_new(b"cbacba");
+    assert_eq!(P_SUCCESS, p_parse(&mut c));
+    assert_eq!(0x932187932187, p_result(&c));
+    p_context_delete(c);
+}