Added support for overriding log handlers for breadcrumbs.
Added support for overriding log handlers for breadcrumbs.

johansteffner/raven-python,akalipetis/raven-python,getsentry/raven-python,getsentry/raven-python,getsentry/raven-python,akalipetis/raven-python,johansteffner/raven-python,johansteffner/raven-python,akalipetis/raven-python