Several doc fixes for events
Add more events to the base type environment

Notably the following are not supported yet:
  - `filesystem-change-evt` (likely needs separate base type)
  - `port-progress-evt` (separate type, and how do you handle
      `port-provides-progress-evts?`?)
  - all other events that rely on progress events

Also, the events from racket/port don't work yet due
to a strange bug with bindings that have contracts imported
into TR's base environment