added a core implementation of FIB tables using generic addresses in an outer table structure
The FIB and the generic addresses operating event driven (no threads for either)
Access to either data is mutually excluded

- the basic functions are implemented for operating FIB tables (add/remove/update entry)
- Reactive Routing Protocols are notified when no destination is available for a next hop request
- generic addresses are implemented using a use_count to trigger if an address can be reused/overwritten
  once allocated memory will remain allocated until calling deintialisation for `generic_address`, pruning all entries
  or when an unsed entry is overwritten with a new entry of distinct size
- FIB tables are statically represented by an array of entries pointing to generic_address entries

TODO:
- test the implementation with the real network layer (tested with RPL on IoT-lab_M3)
- using the type field to recognize/apply compression
  - use compression, e.g. LOWPAN_IPHC

NOTE:
this is a prototype implementation it can be considered as a proof of concept in this state
It follows strictly KISS. So, no fancy algorythms nor code hocus-pocus is applied.