Allow using WASI APIs in the Python extension (#533)

* Allow using WASI APIs in the Python extension

This commit adds support to the Python extension to load the WASI
implementation when a WASI module is seen allowing Python to load
WebAssembly modules that use WASI. This is pretty primitive right now
because there's no way to configure the environment/args/preopens/etc,
but it's hoped to be at least a start!

* rustfmt

* Refactor checks for the wasi module name

* Move the check into `wasmtime-wasi` itself
* Make it conservative for now and match anything that says `wasi*`
* Leave a `FIXME` for improving this later on

* Enable missing feature of winapi for `winx`

crates/misc/py/src/lib.rs

@@ -73,6 +73,15 @@ pub fn instantiate(
     }
 
     let data = Rc::new(ModuleData::new(wasm_data).map_err(err2py)?);
+
+    // If this module expects to be able to use wasi then go ahead and hook
+    // that up into the imported crates.
+    if let Some(module_name) = data.find_wasi_module_name() {
+        let wasi_handle =
+            wasmtime_wasi::instantiate_wasi("", context.get_global_exports(), &[], &[], &[])
+                .map_err(|e| err2py(e.into()))?;
+        context.name_instance(module_name, wasi_handle);
+    }
     let instance = context
         .instantiate_module(None, wasm_data)
         .map_err(|e| err2py(e.into()))?;
@@ -111,6 +120,11 @@ pub fn imported_modules<'p>(py: Python<'p>, buffer_source: &PyBytes) -> PyResult
         let reader = section.get_import_section_reader().unwrap();
         for import in reader {
             let import = import.unwrap();
+            // Skip over wasi-looking imports since those aren't imported from
+            // Python but rather they're implemented natively.
+            if wasmtime_wasi::is_wasi_module(import.module) {
+                continue;
+            }
             let set = match dict.get_item(import.module) {
                 Some(set) => set.downcast_ref::<PySet>().unwrap(),
                 None => {