Initialize Bugsnag exception handler, when desired.
Initialize Bugsnag exception handler, when desired.

At Runscope we use Bugsnag to track application exceptions. This commit allows
you to use Bugsnag to track httpbin exceptions. If you want to do this, you'll
need to set the environment variable BUGSNAG_API_KEY and optionally set the
variable BUGSNAG_RELEASE_STAGE. You'll also need to install the Python client
for Bugsnag, with `pip install bugsnag`.

OndrejPontes/httpbin,Lukasa/httpbin,sigmavirus24/httpbin,pskrz/httpbin,vscarpenter/httpbin,Runscope/httpbin,Lukasa/httpbin,yemingm/httpbin,marinehero/httpbin,Stackato-Apps/httpbin,scottydelta/httpbin,mansilladev/httpbin,nkhuyu/httpbin,postmanlabs/httpbin,shaunstanislaus/httpbin,bradparks/httpbin__http_echo_service_for_testing_http_requests,luosam1123/httpbin,SunGuo/httpbin,mozillazg/bustard-httpbin,fangdingjun/httpbin,mojaray2k/httpbin,hnq90/httpbin,Jaccorot/httpbin,Jaccorot/httpbin,paranoiasystem/httpbin,luhkevin/httpbin,logonmy/httpbin,shaunstanislaus/httpbin,lioonline/httpbin,sigmavirus24/httpbin,logonmy/httpbin,vscarpenter/httpbin,Runscope/httpbin,kennethreitz/httpbin,krissman/httpbin,luhkevin/httpbin,gvangool/httpbin,admin-zhx/httpbin,Stackato-Apps/httpbin,OndrejPontes/httpbin,mozillazg/bustard-httpbin,admin-zhx/httpbin,pestanko/httpbin,marinehero/httpbin,krissman/httpbin,yemingm/httpbin,mojaray2k/httpbin,postmanlabs/httpbin,habibmasuro/httpbin,yangruiyou85/httpbin,hnq90/httpbin,pestanko/httpbin,luosam1123/httpbin,SunGuo/httpbin,fangdingjun/httpbin,habibmasuro/httpbin,scottydelta/httpbin,gvangool/httpbin,phouse512/httpbin,yangruiyou85/httpbin,ewdurbin/httpbin,paranoiasystem/httpbin,lioonline/httpbin,mansilladev/httpbin,phouse512/httpbin,nkhuyu/httpbin,ashcoding/httpbin,pskrz/httpbin,kennethreitz/httpbin,ewdurbin/httpbin,bradparks/httpbin__http_echo_service_for_testing_http_requests,ashcoding/httpbin