Auto merge of #205 - Natim:131-cursor-ret-type-return-option-type, r=emilio
Auto merge of #205 - Natim:131-cursor-ret-type-return-option-type, r=emilio

Make clang::Cursor::ret_type return an Option<Type> — Fixes #131

Well apparently nobody is using  `Cursor::ret_type` 😢

jdub/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,jdub/rust-bindgen,jdub/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,jdub/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen