Clarified usage of node-style function wrappers

- Swapped out invalid `http.get` example in `nodefn.apply` for a
variation on the example in `nodefn.call`.
- Added a note to clarify event emitters do not work with the existing
`when/node/function` api.
Merge pull request #225 from gotdibbs/api-docs-update

Clarified usage of node-style function wrappers