Automatically allow `non_snake_case, non_camel_case_types, non_upper_case_globals`

[crumblingstatue]

Bindings generated by bindgen are not expected to follow Rust naming conventions, so it's a reasonable default to automatically add #![allow(non_snake_case, non_camel_case_types, non_upper_case_globals)] to the generated module.

[fitzgen]

See also #373

[highfive]

Hi! If you have any questions regarding this issue, feel free to make a comment here, or ask it in the #servo channel in IRC.

If you intend to work on this issue, then add @highfive: assign me to your comment, and I'll assign this to you. 😄

[framlog]

@highfive: assign me

[highfive]

Hey @framlog! Thanks for your interest in working on this issue. It's now assigned to you!

[jdm]

Have you made any progress, @framlog? Any questions?

[jdm]

Oh, I missed #580.

[framlog]

@jdm It should works imo.

[emilio]

I don't think we should do that given how invasive it is (see #580). Thanks @framlog, though, for coming up with a PR!