gzip integration

[juvilius]

Overview of New Code/Feature

Relying on the correct file extension for gzip, this uncompresses the input file before giving the data to the parser. The workflow is the exact same as before, hence no new tests or comments

Checklist

• [x] I have read CONTRIBUTING.rst.
• [ ] I have documented any new functions.
• [ ] I have added unit tests for the new code.
• [ ] I have added an integration test (if appropriate).
• [x] I have run all tests. Same errors before and after.
• [x] I am requesting to merge into the appropriate branch.

[samirelanduk]

Great addition - thanks!