Add a tool for looking up hosts information

Format like this:
 root@OpenWrt:/# bwt
 192.168.123.103/0/0///my-pc///Shenzhen Tp-Link Technology Co; Ltd.
                 ^               # downlink speed(KB/s)
                   ^             # uplink speed
                       ^         # host name readed from /tmp/dhcp.leases
                               ^ # vendor name readed from online database

TODO: The database of www.macvendorlookup.com seems a little old,
may be need better one.