releasing strategy for unresponsive and banned peers

[davidmarkclements]

NOTE: This PR is based on #25 - once that is merged this will be much simpler to review

• will write tests once strategy is validated
• defines two "bad peer" types:
  • unresponsive – retry count was exceeded
  • banned - peer has been banned
• exposes queue options at top level
• adds a new forget option to the queue options, where we can define ms wait before removing unresponsive or banned peers. Banned defaults to Infinity - e.g. banned peers are never forgotten by default.
• tiny bit of refactoring to const

[mafintosh]

Looking solid! Asked a question, but that can be resolved later if complex also.