Fix regex to be marked opaque
Fix regex to be marked opaque

While `std::*` makes informal sense, the user may be mislead into calling `opaque_type("std::*")` instead of the correct `opaque_type("std::.*")` (as I was).
rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen