some fixes and rewriting
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)

zwei14/node-arp,nekuz0r/node-arp