(feature request) Present failed connections when finished

[riramar]

First of all thanks a lot for so many useful tools!
I was testing an application and I was sure that meg was missing some requests since testing manually with curl I was getting 200.
Reducing the number of threads solve the problem but I was wondering how many requests meg missed in the past and I didn't know it.
I think if meg was presenting the total number of connections failed it'd help to identify this issue quickly.

[leesoh]

It sounds like this might dovetail with #47