Refactor Connection#exec

* options and options.prefix no longer used in favor of always logging pkg.name
* treat stderr and stdout as the same based on exit code (eg git seems to like stderr)
Refactor .disconnect()

* Put it in its own file like .connect()
* Wait for end-event before done
Use pkg.name for logging in .connect(), and catch potential errors from ssh2#connect
Version bump 0.0.1