Autopub Versions Save

• Remove hard dependency on Poetry, by @apollo13 via #38
• Drop Python 3.6 support

Fix error when creating GitHub releases [PR #28 by Patrick Arminio]

Update github contributor message

Add GitHub PR & contributor info to the changelog [PR #17 by Marco Acierno]

Update dependency specifications to more up-to-date versions

Change minimum Python version from 3.7 to 3.6

Create CHANGELOG file if it does not exist

Ensure AutoPub can be used without installing github_release

Support GitHub Actions

Switch default subprocess output decoding from ASCII to UTF-8.