Remove custom Serde implementation (#44)

* Serialize `BlindedElement` as `GenericArray`

* Don't hold input

* Remove allocations from `VerifiableClient::batch_finalize`

* Remove all allocation from serialization

* Remove required `alloc` support.

* Fix accidental usage of 1.57 API

* Let `VerifiableClient::batch_finalize` return a concrete type

* Simplify de-serialization

* Remove custom Serde implementation

.github/workflows/main.yml

@@ -41,8 +41,8 @@ jobs:
           - ristretto255_u64,p256
         frontend_feature:
           -
-          - --features serde
           - --features danger
+          - --features serde
         toolchain:
           - stable
           - 1.51.0
@@ -64,6 +64,12 @@ jobs:
           command: test
           args: --no-default-features --features ${{ matrix.backend_feature }}
 
+      - name: Run cargo test with alloc
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --no-default-features ${{ matrix.frontend_feature }},alloc --features ${{ matrix.backend_feature }}
+
       - name: Run cargo test with std
         uses: actions-rs/cargo@v1
         with:
@@ -88,8 +94,8 @@ jobs:
           - --features p256
         frontend_feature:
           -
-          - --features serde
           - --features danger
+          - --features serde
     steps:
       - uses: actions/checkout@v2
       - uses: hecrj/setup-rust-action@v1