Overhaul sudo() docstring as DDD re: sudo user
Overhaul sudo() docstring as DDD re: sudo user

- I messed up and left references to a 'prefix' param in place; it was never
  created and doesn't seem useful at this point (a single string prefix would
  be impossible to manage piecemeal, requiring users to reproduce all settings
  to change any one of them!)
- Sections, since it's longer now
- Explicit mention of all sudo CLI flags used
- Cleaned up references to params/configs

pyinvoke/invoke,mkusz/invoke,mkusz/invoke,pyinvoke/invoke