Implemented no_std support (with/without alloc)

.github/workflows/ci.yml

@@ -14,6 +14,11 @@ jobs:
           - stable
           - beta
           - nightly
+        features:
+          - --no-default-features
+          - --features alloc --no-default-features
+          - --features default
+          - --all-features
     steps:
       - name: Checkout sources
         uses: actions/checkout@v2
@@ -30,13 +35,13 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: build
-          args: --all --all-features
+          args: ${{ matrix.features }}
 
       - name: Test
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --all-features
+          args: ${{ matrix.features }}
 
       - name: Lint
         uses: actions-rs/cargo@v1

Cargo.toml

@@ -35,7 +35,16 @@ rmp-serde = { version = ">=1", default-features = false, optional = true }
 trybuild = { version = "1.0", features = ["diff"] }
 
 [features]
-default = ["derive"]
+default = ["std", "derive"]
+
+# Provide impls for common standard library types like Vec<T> and HashMap<K, V>.
+# Requires a dependency on the Rust standard library.
+std = ["alloc"]
+
+# Provide impls for types in the Rust core allocation and collections library
+# including String, Box<T>, Vec<T>, and Cow<T>. This is a subset of std but may
+# be enabled without depending on all of std.
+alloc = []
 
 # Provides a `derive` macro for implementing the `Transient` trait
 derive = ["transient-derive"]