.gitignore
arrow: Remove distinct widget type
arrow: eliminate Widget type alias
arrow: Eliminate embed function
arrow: eliminate custom widget chain operation

Now it's just an alias to nest.
arrow: eliminate |^ opeator in favor of |-
arrow: rewrite bind to not take a context argument

The context is already implicit in the returned Selection, so there's no
need to take it as an argument. This means that you can rewrite this:

  selectAll "circle"
  |= (\_ -> ...)

... as this instead:

  selectAll "circle"
  |. bind (\_ -> ...)

For now (|=) takes an additional context argument to maintain
compatibility with existing example code.
arrow: update export comments
arrow: update module documentation