Add hashes 0.14 to the dependency range

We just release a new version of `bitcoin_hashes` which works with
`bip39` with no changes.

Add `bitcoin_hashes v0.14` to the dependency range and document its
effect on the MSRV.

(Note, the "alloc" feature is required as of 0.14).

Cargo.toml

@@ -49,11 +49,11 @@ serde = { version = "1.0", default-features = false, features = [ "alloc" ], opt
 zeroize = { version = "1.5", features = ["zeroize_derive"], optional = true }
 
 # Unexported dependnecies
-bitcoin_hashes = { version = ">=0.12, <=0.13", default-features = false }
+bitcoin_hashes = { version = ">=0.12, <=0.14", default-features = false, features = ["alloc"] }
 unicode-normalization = { version = "=0.1.22", default-features = false, optional = true }
 
 [dev-dependencies]
-bitcoin_hashes = ">=0.12,<0.14" # enable default features for test
+bitcoin_hashes = ">=0.12,<=0.14" # enable default features for test
 
 
 [package.metadata.docs.rs]

README.md

@@ -35,6 +35,7 @@ The `bitcoin_hashes` range dependency effects the MSRV as follows
 
 - `bitcoin_hashes v0.12`: MSRV v1.41.1
 - `bitcoin_hashes v0.13`: MSRV v1.48.0
+- `bitcoin_hashes v0.14`: MSRV v1.56.1
 
 When using older version of Rust, you might have to pin the version of the
 `bitcoin_hashes` crate used as such:

src/internal_macros.rs

@@ -10,6 +10,7 @@ macro_rules! serde_string_impl {
 			{
 				use core::fmt::{self, Formatter};
 				use core::str::FromStr;
+				#[cfg(feature = "alloc")]
 				use alloc::string::String;
 
 				struct Visitor;
@@ -34,6 +35,7 @@ macro_rules! serde_string_impl {
 						self.visit_str(v)
 					}
 
+					#[cfg(feature = "alloc")]
 					fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
 					where
 						E: $crate::serde::de::Error,