Add method to get a PurpleAir map URL

[bachya]

Describe what the PR does:

SSIA

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests are written for the new functionality.
• Run tests and ensure everything passes (with 100% test coverage).
• Update README.md with any new documentation.
• Add yourself to AUTHORS.md.

[codeclimate]

Code Climate has analyzed commit 8a118ec and detected 0 issues on this pull request.

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[codecov]

Codecov Report

Merging #34 (8a118ec) into dev (e313f84) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev       #34   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines          502       505    +3     
=========================================
+ Hits           502       505    +3     

Impacted Files	Coverage Δ
aiopurpleair/api.py	100.00% <100.00%> (ø)

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