Allow faster traceroute parsing with optional minimalist hop-parsing …

[chrisamin]

• This adds support for a "parse_all_hops=False" option to Traceroute.init which will start at the last hop, and work backwards only as long as is necessary to fill in the various Traceroute-level attributes, such as last_hop_responded, destination_ip_responded and last_median_rtt. This is useful for cases when we don't need access to the actual hops, because it saves on a lot of object initialization for all of the extra Hop and Packet objects.
• The request also removes the use of IPy to compare the intended destination address with the origin reported in the last hop, because these should always be in canonical form. I spoke with @PhilipHomburg who says he would consider it a bug if there was ever a difference in IPv6 address representation within the traceroute results.

[danielquinn]

Looks good to me, but you should update the changelog if you're changing dependencies like this.

[astrikos]

Looks good to me as well. merging...