Improve logging

[jifeon]

Need to log messages on several levels, such as error, warning, info, debug etc. It's very important to log requests and responses on most verbose level.

Also want to mention specific situation: if API returns not JSON with application/json header then all you see in console is just a mention about URL and the fact JSON has not parsed. I think in this situation not only original error should be logged but also whore response.body