Bump MSRV to 1.56.1

As we have done in other parts of the ecosystem bump the MSRV to Rust
`v1.56.1`.

Done for `secp256k1` and `secp256k1-sys`.

.github/workflows/rust.yml

@@ -55,15 +55,15 @@ jobs:
         run: ./contrib/test.sh
 
   MSRV:
-    name: Test - 1.48.0 toolchain
+    name: Test - 1.56.1 toolchain
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v3
       - name: Checkout Toolchain
-        uses: dtolnay/rust-toolchain@1.48.0
+        uses: dtolnay/rust-toolchain@1.56.1
       - name: Running test script
         env:
           DO_FEATURE_MATRIX: true

Cargo.toml

@@ -10,7 +10,8 @@ documentation = "https://docs.rs/secp256k1/"
 description = "Rust wrapper library for Pieter Wuille's `libsecp256k1`. Implements ECDSA and BIP 340 signatures for the SECG elliptic curve group secp256k1 and related utilities."
 keywords = [ "crypto", "ECDSA", "secp256k1", "libsecp256k1", "bitcoin" ]
 readme = "README.md"
-edition = "2018"
+edition = "2021"
+rust-version = "1.56.1"
 
 [package.metadata.docs.rs]
 all-features = true

README.md

@@ -29,7 +29,7 @@ Contributions to this library are welcome. A few guidelines:
 * Any breaking changes must have an accompanied entry in CHANGELOG.md
 * No new dependencies, please.
 * No crypto should be implemented in Rust, with the possible exception of hash functions. Cryptographic contributions should be directed upstream to libsecp256k1.
-* This library should always compile with any combination of features on **Rust 1.48.0**.
+* This library should always compile with any combination of features on **Rust 1.56.1**.
 
 ### Githooks
 

secp256k1-sys/Cargo.toml

@@ -13,7 +13,8 @@ keywords = [ "secp256k1", "libsecp256k1", "ffi" ]
 readme = "README.md"
 build = "build.rs"
 links = "rustsecp256k1_v0_9_2"
-edition = "2018"
+edition = "2021"
+rust-version = "1.56.1"
 
 [package.metadata.docs.rs]
 all-features = true

secp256k1-sys/README.md

@@ -49,4 +49,4 @@ to your `RUSTFLAGS` variable.
 
 ## Minimum Supported Rust Version
 
-This library should always compile with any combination of features on **Rust 1.48.0**.
+This library should always compile with any combination of features on **Rust 1.56.1**.