Removing print and adding a logger

[chayim]

Thank you for the awesome project! As part of my use, I noticed a tonne of print statements, whenever I run my tests. This is getting in the way of debugging. As a result, I integrated a logger. For every (non-thirdparty) statement present, I replaced print with log. When the error text indicated a level (eg. warning, error), I used that log level.

When no level was specified I defaulted to DEBUG, which now, will not print.

Should someone want debug, they merely have to set the environment variable DEBUG to any value.

Thanks again for a great project, I hope this is useful to someone else, given #2481

[Jimmy-ajia]

您好，我已经收到您的邮件，尽快给您回复。

[GreatNewWorldDev]

@nttstar Hi, this PR seems to improve the current logging approach by using a dedicated logger with a INFO default log level which will allow to filter out repetitive, debug logs which usually just clutter the console while allowing to specify an environment variable to see debug logs when needed for debugging. So it would be great if you have time to review this small PR, see if can be merged or needs adjustments. Thanks for your attention!