Implement backoff

[akdor1154]

This implements exponential backoff for all Sumologic API calls.

There is also a fix for the endpoint patch that made its way in recently that didn't seem to be tested properly (ping @mccartney), this and a whitespace fix are in separate commits, hope that's OK.

Cheers
Jarrad

[akdor1154]

This should fix #3 .

[rickjuryxero]

this is a great idea - we have been having rate limiting issues trying to build something on top of this sdk. It would be great to have this fixed inside the python sdk

[himanshu219]

Actually request library itself implements exponential backoff we need to pass few parameters to it. Though the solution looks good any specific reason for creating the custom backoff function instead of using builtin solution https://www.peterbe.com/plog/best-practice-with-retries-with-requests

[akdor1154]

Oh cool. Happy to go with whatever Sumo team prefer.

[dspruell-s01]

Looking at implementing an API client integration with this library - any prospects for having this bumped/merged soon?