Support to choose the logging interface

[bnkamalesh]

By default the logs are printed to stdout. Though, there should be a provision of providing an output of users' choice. Need to update the logging mechanism to use an interface, so that it can be set to a thirdparty/external logger

• Convert current logs to use an interface
• Expose a method to replace the logging interface on the fly (should be concurrency safe)

[bnkamalesh]

https://github.com/bnkamalesh/webgo/releases/tag/2.4.0