Support for choosing between encryption mechanisms

Currently supports GPG or keybase.
Merge pull request #13 from rvlvvr/encryption-backends

Support for choosing between encryption mechanisms
fixed dual join bug
updated errors msgs and readme
updated small info about windows
🚧 WIP 🚧 - First cut at putting connected users on top.
Merge remote-tracking branch 'upstream/master'
Seems to work.