Update bindgen to version 0.22

[prokopyl]

This commit updates bindgen to version 0.22, enabling support for newer Clang versions (3.6 to 3.9).

The transition to bindgen >= 0.20 brings a few changes, but the biggest one is the fact that the Builder::remove_prefix method has not been re-implemented (and it seems they don't plan to re-implement it, at least not this way, see rust-lang/rust-bindgen#428), therefore breaking the v8-sys API, as all the v8::function are now v8::v8_function.
However, I don't think this is a big deal, as the v8-sys API isn't stable yet, and a -sys crate isn't supposed to have a pretty API anyway. Obviously, this commit updates v8 crate in order to take this change into account, hence the pretty big diff.

The other (non-breaking) changes this transition brings are :

• bindgen now understands that some parameters are actually booleans, so several 0s/1s have been replaced by trues/falses accordingly;
• Similarily, some usize types are now u64.
• Clang now emits clang::TypeKind::Elaborated (since 3.9 I believe), and recognises v8's Local<> types as such, so the build.rs script has been updated to handle both cases.

[dflemstr]

Looks good! 👍