Add #![allow(dead_code)] in generated *.rs files

[hicqu]

There are a lot of method is never used: Something when cargo build.

So, I think we need #![allow(dead_code)]. What do you think?

[dwrensha]

Unfortunately, putting #![allow(dead_code)] at the top of generated files would interfere with include!(): rust-lang/rust#18810

We could put #[allow(dead_code)] on every generated item, but that seems ugly.

So, I recommend that you add the #[allow(dead_code)] attribute yourself, at the location in the code where you include!() the generated code.

[hicqu]

OK, I will try do that in build.rs. Thank you!