Support Packet Loss Statistics

[samgomena]

Is your feature request related to a problem? Please describe.
I have a use case for determining the packet loss percentage from a ping request. I don't believe this library supports that.

Describe the solution you'd like
I would like to be able to determine the percentage of packets lost in a ping request. Similar to how a successful ping can be determined:

# Supported
ping("localhost").success()

# Not supported
pint("localhost").packet_loss()

Describe alternatives you've considered
I've forked the library and have what I think is a naive implementation:

# In executor.py > ResponseList
def packet_loss(self):
    success_list = [resp.success for resp in self._responses]
    return (success_list.count(False) / len(success_list)) * 100

Additional context
I noticed there was a comment on another issue where someone mentioned they were also interested in determining packet loss. If this is a feature that you would be willing to add to the library, I'd be more than happy to submit a PR for it!

[alessandromaggio]

This is an interesting that would definitely be beneficial to a lot of people. If you make a PR for it I'll be glad to integrate it in the next release.

Please let me make some considerations on the implementation:

1. The rate must be normalized in a 0-1 range (0% loss represented as 0.0, 100% loss as 1.0)
2. Instead of computing a normal average by interating again on all the data after the ping results come in, compute a running average while the data comes in, so that reading the packet_loss() property will only return that value without having to do additional computation.

Thank you!

[alessandromaggio]

Included in release 1.0.15, already out. Thank you @samgomena!