Modernize our auto-reconnecting wrapper for `WebSocket` to match current
conventions in the client and improve the documentation.

 - Use named rather than default exports
 - Convert functions to arrow functions and remove unneeded `self`
   alias.
 - Add JSDoc comments and types

A circular reference between the `connect` and `onAbnormalClose`
functions was broken by adding a second argument to `onAbnormalClose`.