Some fixes and rewriting

- FIX : arp command for OSX (-n not -an)
- MODIFY : rewrite Linux lookup function to avoid looping over all entries and returned lines (arp -n IPADDRESS)
- MODIFY : rewrite OSX lookup function to avoid looping over all returned lines
- FIX : OSX formates double zero as a single one (i.e : 0:19:99:50:3a:3 instead of 00:19:99:50:3a:3)
- FIX : lookup functions did not returns the function on error causing callback to be called twice
- FIX : Windows lookup function returns wrong mac address due to indexOf usage (192.168.1.1 -> 192.168.1.10)