* Tweak the implementation of heap closures
This commit updates the implementation of the `Closure` type to internally store
an `Rc` and be suitable for dropping a `Closure` during the execution of the
closure. This is currently needed for promises but may be generally useful as
well!
* Support asynchronous tests
This commit adds support for executing tests asynchronously. This is modeled
by tests returning a `Future` instead of simply executing inline, and is
signified with `#[wasm_bindgen_test(async)]`.
Support for this is added through a new `wasm-bindgen-futures` crate which is a
binding between the `futures` crate and JS `Promise` objects.
Lots more details can be found in the details of the commit, but one of the end
results is that the `web-sys` tests are now entirely contained in the same test
suite and don't need `npm install` to be run to execute them!
* Review tweaks
* Add some bindings for `Function.call` to `js_sys`
Name them `call0`, `call1`, `call2`, ... for the number of arguments being
passed.
* Use oneshots channels with `JsFuture`
It did indeed clean up the implementation!
* Create bindings for RegExp
* Address review comments
- Split the constructor into two: `new` and `new_regexp`. This way we
can write RegExp::new("foo", "g") rather than
RegExp::new(&JsValue::from("foo"), "g").
- The js_name for the setter for lastIndex should be `lastIndex` and
not `set_lastIndex`. But fixing this causes a panic. Remove the
method for now.
