Derive additional traits for error type

Back in February this year I must have been mad, commit:

 `commit 2bbfc28`

removed all the derives from the error type except `Debug`. This makes
the error type un-ergonomic to use downstream - bad Tobin, no biscuit.

Derive what has become our standard set of derives for error types in
the `rust-bitcoin` eccosystem. Also include `Copy` because this error is
exhaustive.

Author: tcharding

src/lib.rs

@@ -167,7 +167,7 @@ pub mod ffi {
 ///
 /// [`libbitcoinconsensus`]: <https://github.com/bitcoin/bitcoin/blob/master/doc/shared-libraries.md#errors>
 #[allow(non_camel_case_types)]
-#[derive(Debug)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
 #[repr(C)]
 pub enum Error {
     /// Default value, passed to `libbitcoinconsensus` as a return parameter.