Inline docs for threepio.py

[Praful932]

Description

• Added inline documentation and docstrings for threepio.py
• Fixed flake8 warnings
• removed deprecated function parameters

Resolves #69

I have followed restructured text format to document the code same as Pysyft docs

Affected Dependencies

None

How has this been tested?

Passed pytest and flake8 as described in the workflow file.

Checklist

• [X] I have followed the Contribution Guidelines and Code of Conduct
• [ ] I have commented my code following the OpenMined Styleguide
• [ ] I have labeled this PR with the relevant Type labels
• [X] My changes are covered by tests

[Praful932]

@Nolski The Openmined styleguide mentions Google Doc style while Pysyft uses rst format for docs. To keep it consistent with Pysyft I used rst format, let me know if I need to change the doc style

[ramesht007]

Looks good to me :) Thanks, @Praful932