Refactor the types.rs types and structures (#681)

* Refactor the `types.rs` types and structures

A few changes applied along the way:

* Documentation added to most methods and types.
* Limits are now stored with the maximum as optional rather than a
  sentinel u32 value for `None`.
* The `Name` type was removed in favor of just using a bare `String`.
* The `Extern` prefix in the varaints of `ExternType` has been removed
  since it was redundant.
* Accessors of `ExternType` variants no longer panic, and unwrapping
  versions were added with "unwrap" in the name.
* Fields and methods named `r#type` were renamed to `ty` to avoid
  requiring a raw identifier to use them.

* Remove `fail-fast: false`

This was left around since the development of GitHub Actions for
wasmtime, but they're no longer needed!

* Fix compilation of the test-programs code

* Fix compilation of wasmtime-py package

* Run rustfmt

crates/misc/py/src/lib.rs

@@ -111,21 +111,18 @@ pub fn instantiate(
 
     let mut imports: Vec<wasmtime::Extern> = Vec::new();
     for i in module.borrow().imports() {
-        let module_name = i.module().as_str();
+        let module_name = i.module();
         if let Some(m) = import_obj.get_item(module_name) {
-            let e = find_export_in(m, &store, i.name().as_str())?;
+            let e = find_export_in(m, &store, i.name())?;
             imports.push(e);
         } else if wasi.is_some() && module_name == wasi.as_ref().unwrap().0 {
             let e = wasi
                 .as_ref()
                 .unwrap()
                 .1
-                .find_export_by_name(i.name().as_str())
+                .find_export_by_name(i.name())
                 .ok_or_else(|| {
-                    PyErr::new::<Exception, _>(format!(
-                        "wasi export {} is not found",
-                        i.name().as_str()
-                    ))
+                    PyErr::new::<Exception, _>(format!("wasi export {} is not found", i.name(),))
                 })?;
             imports.push(e.clone());
         } else {