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
You could use ```if [[ $EUID -eq 0 ]]; then``` to check for the effective user id to be 0.
When using sudo the effective user id changes to 0 (normally).
Prohibiting su or sudo might fail the goal, when the target user of these commands is not root. This way the user would be denied, although he/she is not root