For simplicity (avoid parsing), escape sequences and raw string literals
are not yet handled.

Module names, aliases and license strings are restricted to ASCII only.

Link: Rust-for-Linux#252
Link: https://lore.kernel.org/lkml/YukvvPOOu8uZl7+n@yadro.com/
Signed-off-by: Gary Guo <gary@garyguo.net>