better exception logging

[b-ryan]

The way this library currently logs exception is completely unreadable. It spits out a one-line JSON blob. This change passes the exception as the first arg to log/error in order to print stack traces.

With this change, whatever was being accomplished with the MDC handling is lost. I am hoping I can get some insight into why it was there and if I should add it back.

Currently, this is not functionally tested.

[b-ryan]

ping @bpiel

[bpiel]

approved

[b-ryan]

boom