Add google-style docstrings (issue #532).

[tonyskapunk]

Description

• Add Google-style doc-strings to memory.py
• Partially fixes Add Google Style Docstrings #532

Starting with an easy one and moving along as soon as I get some feedback. Thanks!

Status

READY

Type of change

• Documentation (fix or adds documentation)

How Has This Been Tested?

Validate the docstrings through pydoc: https://gist.github.com/tonyskapunk/0440271eed357fdd31befd476f017691

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works

[codecov]

Codecov Report

Merging #693 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #693   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          23     23           
  Lines        1460   1460           
=====================================
  Hits         1460   1460

Impacted Files	Coverage Δ
opsdroid/memory.py	100% <ø> (ø)	⬆️

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[jacobtomlinson]

This is awesome many thanks!

[jacobtomlinson]

Ping me your address via DM on Twitter or Gitter and I'll post you some opsdroid stickers!