Add Python 3.5.3 support

[bachya]

Describe what the PR does:

This PR adds Python 3.5.3 as a supported version. This is principally done to support the current requirement that Home Assistant supports 3.5.3.

NOTE: aresponses (which the library currently uses for aiohttp testing) uses literal string interpolation, which requires Python 3.6. Therefore, although the library "supports" 3.5.3, testing (and anything related to testing, including Travis) must have a minimum of 3.6.

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests is written for the new functionality.
• Update README.md with any new documentation.
• Run tests and ensure 100% code coverage: make coverage (after running make init)
• Ensure you have no linting errors: make lint (after running make init)
• Ensure you have no typed your code correctly: make typing (after running make init)
• Add yourself to AUTHORS.md.

[codecov]

Codecov Report

Merging #12 into dev will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##            dev    #12   +/-   ##
===================================
  Coverage   100%   100%           
===================================
  Files         5      5           
  Lines       247    247           
===================================
  Hits        247    247

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