VRF structure (#171)

* added unique name for locRIBs

* added VRFs

* added error when no RIB configured in VRF

* vrf unique name ensurance

* fixed examples

* added missing test

* for convenience we provide a default RIB for v4 and v6 on each VRF

* removed debug output in main.go (api is coming)

* also removed debug output from fib example

* removed fib example