Clean up hashes import statements

Now that we have `hashes` as the crate name of `bitcoin_hashes` we can
slightly clean up the import statements.

This is based on the convention we have to import things directly from
the crate if we depend on it and not from the crate level re-export.

src/lib.rs

@@ -175,6 +175,8 @@ use core::{fmt, mem, str};
 
 #[cfg(feature = "global-context")]
 pub use context::global::SECP256K1;
+#[cfg(feature = "hashes")]
+use hashes::Hash;
 #[cfg(feature = "rand")]
 pub use rand;
 pub use secp256k1_sys as ffi;
@@ -184,8 +186,6 @@ pub use serde;
 pub use crate::context::*;
 use crate::ffi::types::AlignedType;
 use crate::ffi::CPtr;
-#[cfg(feature = "hashes")]
-use crate::hashes::Hash;
 pub use crate::key::{PublicKey, SecretKey, *};
 pub use crate::scalar::Scalar;
 
@@ -1016,16 +1016,16 @@ mod tests {
     #[cfg(feature = "hashes")]
     #[test]
     fn test_from_hash() {
-        use crate::hashes::{self, Hash};
+        use hashes::{sha256, sha256d, Hash};
 
         let test_bytes = "Hello world!".as_bytes();
 
-        let hash = hashes::sha256::Hash::hash(test_bytes);
+        let hash = sha256::Hash::hash(test_bytes);
         let msg = Message::from(hash);
         assert_eq!(msg.0, hash.to_byte_array());
         assert_eq!(msg, Message::from_hashed_data::<hashes::sha256::Hash>(test_bytes));
 
-        let hash = hashes::sha256d::Hash::hash(test_bytes);
+        let hash = sha256d::Hash::hash(test_bytes);
         let msg = Message::from(hash);
         assert_eq!(msg.0, hash.to_byte_array());
         assert_eq!(msg, Message::from_hashed_data::<hashes::sha256d::Hash>(test_bytes));

src/secret.rs

@@ -35,7 +35,7 @@ macro_rules! impl_display_secret {
         #[cfg(all(not(feature = "std"), feature = "hashes"))]
         impl ::core::fmt::Debug for $thing {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
-                use crate::hashes::{sha256, Hash, HashEngine};
+                use hashes::{sha256, Hash, HashEngine};
 
                 let tag = "rust-secp256k1DEBUG";