Add Rust target

spec/test_user_context_fields.rs

@@ -0,0 +1,9 @@
+use testparser::*;
+
+fn main() {
+    let mut c = p_context_new(b"aaa\n\n\na\n    # comment 1\na  a    aa\n\naa\n#    comment 2\na\n");
+    assert_eq!(P_SUCCESS, p_parse(&mut c));
+    eprint!("comments: {}", c.comments);
+    eprintln!("acount: {}", c.acount);
+    p_context_delete(c);
+}