Refactor the code as per python3 standards

[thejasmeetsingh]

Hey @vividvilla @knadh

As per the readme, from v5, pykiteconnect won't support Python 2.7. And I can see code where the Python2 style of code is still being used. Shouldn't we refactor the code so that it follows the latest Python 3 standards?

Let me know if you agree with this, and if yes, then please assign this issue to me.

Actually, I'm starting my open-source contribution journey, and I would really love to contribute here. Don't worry, I know the drill. I'll fork the project first, work on a separate branch, and then raise the PR to the master branch on the main repo.