Add WASM support for executor

* Adds an executor for WASM runtimes based on wasm_bindgen.
* Add time driver based on JS time handling.
* Add example that can run in browser locally.
* Update to critical-section version that supports 'std' flag

examples/wasm/README.md

@@ -0,0 +1,26 @@
+# WASM example
+
+Examples use a CLI tool named `wasm-pack` to build this example:
+
+```
+cargo install wasm-pack
+```
+
+## Building
+
+To build the example, run:
+
+```
+wasm-pack build --target web
+```
+
+## Running
+
+To run the example, start a webserver server the local folder:
+
+
+```
+python -m http.server
+```
+
+Then, open a browser at https://127.0.0.1:8000 and watch the ticker print entries to the window.