Make the UEFI enums extensible

Some UEFI enums are meant to be extended by the user or the
firmware. This commit ensures this is possible by marking
the field containing the enum value as `pub`.

Closes #59

Author: GabrielMajeri

src/data_types/enums.rs

@@ -53,7 +53,7 @@ macro_rules! newtype_enum {
         $(#[$type_attrs])*
         #[repr(transparent)]
         #[derive(Clone, Copy, Eq, PartialEq)]
-        pub struct $type($base_integer);
+        pub struct $type(pub $base_integer);
 
         $(#[$impl_attrs])*
         #[allow(unused)]