Add runtime support for Python 3.5.3

[bachya]

Describe what the PR does:

This PR adds runtime support for Python 3.5. Note that tests need Python 3.6+ to run.

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 typed your code correctly: make typing (after running make init)

[codecov]

Codecov Report

Merging #3 into dev will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##            dev     #3   +/-   ##
===================================
  Coverage   100%   100%           
===================================
  Files         4      4           
  Lines        63     63           
===================================
  Hits         63     63

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