Add tokio feature & make tokio optional for WASM support (#1382)

* add server feature and make tokio and hyper/server and tcp optional

* address review comments

* don't mention any specific runtimes in the example

* sort deps

* add `tokio` feature when adding `ws`

* don't always pull in tower feature that pulls in tokio io stuff

* remove usage of `tokio_cr`

* changelog

* depend on tokio version that supports wasm

* don't make it sound like tokio doesn't support wasm

* call out new default feature

Co-authored-by: Fisher Darling <[email protected]>
Co-authored-by: David Pedersen <[email protected]>

.github/workflows/CI.yml

@@ -209,6 +209,26 @@ jobs:
           -p axum-macros
           --target armv5te-unknown-linux-musleabi
 
+  wasm32-unknown-unknown:
+    needs: check
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: stable
+        target: wasm32-unknown-unknown
+        override: true
+        profile: minimal
+    - uses: Swatinem/rust-cache@v1
+    - name: Check
+      uses: actions-rs/cargo@v1
+      with:
+        command: check
+        args: >
+          --manifest-path ./examples/simple-router-wasm/Cargo.toml
+          --target wasm32-unknown-unknown
+
   dependencies-are-sorted:
     runs-on: ubuntu-latest
     strategy: