native: create tap interfaces ad-hoc

PR currently only works in Linux, I will add support for other systems once the concept is ACK'd.

Usage: ignore `tapsetup.sh`, just use `make term` and get as many tap interfaces as you need.

TODO:
- [x] don't create unless term target is given
- [ ] integrate support for OSX/FreeBSD
- [ ] update documentation
http://www.sudo.ws/sudo.man.html
"sudo allows a permitted user to execute a command as the superuser or another user, as specified by the security policy."

I never did this before, but seems like you can configure sudo to have another target user than root.
I am not sure about su, but it would not surprise me if theres also a similar feature.
Maybe an alias like "su" as "su <some_other_user>" would break your code? Not sure :)