Clean Up googleapiclient Files

Proposal
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* Improve docstrings and readability of documentation within all files of `googleapiclient`
* Update copyright years on all applicable files

Reasoning
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The docstring updates provide a better understanding of the code when it is displayed in a more organized and uniform fashion. Better understanding of code means improved usability.

The copyright years were updated because the code is actively being used (this project is not dead). The only file whose copyright was not changed was `mimeparse.py` as it was copyrighted by Mr. Joe Gregorio and not by Google.