Update to latest release of bindgen

Note that all of the enum definitions changed (again?), and now they are
flattened into the 'bindings' namespace. This breaks the API in a way that
is relatively easy to fix, albeit annoying. Attempts to change the enum
generation using default_enum_style() resulted in endless compiler errors.

cargo test passes

src/conversions.rs

@@ -22,9 +22,9 @@ pub trait FromRust<T> {
 impl FromRust<bool> for bindings::MagickBooleanType {
     fn from_rust(b: bool) -> Self {
         if b {
-            bindings::MagickBooleanType::MagickTrue
+            bindings::MagickBooleanType_MagickTrue
         } else {
-            bindings::MagickBooleanType::MagickFalse
+            bindings::MagickBooleanType_MagickFalse
         }
     }
 }