Update and improve crate features in web-sys

* Regenerate the list of features for the crate given recent
  improvements, enabling some more types to be bound.
* Add feature gates for the `css` and `console` namespaces (modules),
  gating the APIs by default. Now `web_sys` has zero APIs unless they're
  requested.
* Improved the "required feature" documentation for `struct` types to
  not list parent classes and mention just the `struct` type instead.

examples/console_log/Cargo.toml

@@ -8,4 +8,4 @@ crate-type = ["cdylib"]
 
 [dependencies]
 wasm-bindgen = { path = "../.." }
-web-sys = { path = '../../crates/web-sys' }
+web-sys = { path = '../../crates/web-sys', features = ['console'] }