Bump elliptic-curve to v0.10; MSRV 1.51+ (#268)

Also updates the following:
- `p256` v0.9
- `p384` v0.8

.github/workflows/ci.yml

@@ -36,13 +36,13 @@ jobs:
             toolchain: stable
             deps: true
           - platform: ubuntu-latest
-            toolchain: 1.47.0 # MSRV
+            toolchain: 1.51.0 # MSRV
             deps: sudo apt-get install libpcsclite-dev
           - platform: windows-latest
-            toolchain: 1.47.0 # MSRV
+            toolchain: 1.51.0 # MSRV
             deps: true
           - platform: macos-latest
-            toolchain: 1.47.0 # MSRV
+            toolchain: 1.51.0 # MSRV
             deps: true
     runs-on: ${{ matrix.platform }}
     steps:
@@ -82,8 +82,8 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: 1.47.0 # MSRV
+          toolchain: 1.51.0 # MSRV
           components: clippy
           override: true
       - run: sudo apt-get install libpcsclite-dev
-      - run: cargo clippy --all --exclude crypto_box --all-features -- -D warnings
+      - run: cargo clippy --all --all-features -- -D warnings