Thread Pool

[mav8557]

Right now three goroutines are spawned per user, per box. This is a lot and will get slow with a large network.

A thread pool architecture can help. A certain number of threads, passed as configuration, are spawned at the beginning, and pull Jobs from the same channel. Each Job represents a connection attempt against a particular box, including the Username, IP, and protocol (SSH, SMB, winrm, etc).

[mav8557]

Following up a year later while cleaning this up - an Async implementation would probably work for this also, and likely better. It's a good first tool facelift project, implementing both of these and testing to see which is truly fastest in practice.