debug mode

[gorsuch]

Noticed this while troubleshooting #46 it would make a lot of sense if canary had a flag to enable "debug mode". In this world, I'd like to see the request body emitted as well as the response info.

It would certainly make it easier to see what exactly is going wrong w/o having to resort to a series of log statements.

[blalor]

Might've helped me with #51, too. :-) How do you feel about using logrus for a logger? Then the log level may be configured at runtime, then. Given that there are currently no external dependencies in canary, I understand the resistance to making it a requirement, but if canary had some kind of pluggable logging config, that may make it easier.