Multi-Session Support

[calebstewart]

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
There has been interest in allow pwncat to manage multiple sessions. This hasn't been a priority for me since I didn't personally see the benefit and it requires a lot of changes in pwncat. However, while implementing the impending multi-platform support (#67 for reference), I moved to a manager-based framework which has the concept of sessions built-in. With this change, it should be trivial to bake multi-session support into the new version of pwncat.

While I believe I will definitely be able to incorporate multi-session support, background jobs are going to require some more work. The work on background jobs won't be started until the platform changes are completed as these are two big lifts.

Describe alternatives you've considered
My personal opinion is that utilizing the OS built-in multi-session support is better (i.e. tmux, screen or simply opening multiple terminals). That being said, interest has been expressed in this as a first-class feature in pwncat, so I'll do what I can to support the request.

[calebstewart]

This was added to in the platforms branch, and solved with the merge: 3f799dd.