adding detached parameter

This will prevent the process from hanging while prompting for a password. Specifically, the process no longer has access to /dev/tty.

http://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options
Merge pull request #1 from jaredly/patch-1

adding detached parameter
add exitCode parameter for callback
fix a bug which broke tests
update docs
add travis config
add build status
zap commented code. that's what VCS is for.