Fix compilation of doctests

Tested with:

    CARGO_PROFILE_DEV_PANIC=unwind \
        cargo test -Zbuild-std=std --target x86_64-unknown-linux-gnu

(Changing panic to unwind avoids
rust-lang/wg-cargo-std-aware#56)

Author: nicholasbishop

src/data_types/enums.rs

@@ -30,8 +30,9 @@
 ///
 /// Usage example:
 /// ```
+/// use uefi::newtype_enum;
 /// newtype_enum! {
-/// #[derive(Cmp, PartialCmp)]
+/// #[derive(Ord, PartialOrd)]
 /// pub enum UnixBool: i32 => #[allow(missing_docs)] {
 ///     FALSE          =  0,
 ///     TRUE           =  1,

src/data_types/guid.rs

@@ -97,8 +97,9 @@ impl fmt::Display for Guid {
 /// textual format as an argument, and is used in the following way:
 ///
 /// ```
+/// use uefi::unsafe_guid;
 /// #[unsafe_guid("12345678-9abc-def0-1234-56789abcdef0")]
-/// type Emptiness = ();
+/// struct Emptiness;
 /// ```
 pub unsafe trait Identify {
     /// Unique protocol identifier.

src/proto/mod.rs

@@ -18,6 +18,8 @@ use crate::Identify;
 /// protocol's GUID using the following syntax:
 ///
 /// ```
+/// #![feature(negative_impls)]
+/// use uefi::{proto::Protocol, unsafe_guid};
 /// #[unsafe_guid("12345678-9abc-def0-1234-56789abcdef0")]
 /// #[derive(Protocol)]
 /// struct DummyProtocol {}