Support debug logging for client/CLI

[Jim Baker]

It should be feasible to turn on (and subsequently off) debug logging for the client. The most important debugging is presumably http, but we may have other debugging support that we would want to enable in the future.

The following options should be available to do this setup. The order is in terms of override: a CLI option overrides the env var CRATON_DEBUG, etc.

1. environment variable: CRATON_DEBUG=all|http|none # this can be a list of options; all implies all of them!
2. CLI option: --debug=all|none|http
3. cratonclient.v1.client.Client.debug(*options) # supports dynamic turning on/off; and is used by the above for actual implementation

To support http debugging, we can set up logging for the underlying requests and its libraries:

http://stackoverflow.com/questions/10588644/how-can-i-see-the-entire-http-request-thats-being-sent-by-my-python-application