Add config option to omit __details__

[richmolj]

The __details__ payload is good because it better matches rails, but has the downside of duplicating the information already present in __raw_error__. My thought is we should make this a configuration option, disabling __details__ by default.

[wagenet]

FWIW, it's not a complete duplicate. It can have the backtrace filtered in multiple ways, which might be useful for debugging.