Update REST API docs.

- Somehow "timeout" and "priority" got merged (description of "priority"
  was on "timeout" and "priority" was missing).
- Add the "tags" parameter to `tasks_create_url`.
- `tasks_view` and `machines_view` do not return lists.
- Add new fields to `machines_list` and `machines_view`.
Merge pull request #145 from MITRECND/rest_api_docs

REST API Docs