Automatically configure version information after every chagelog generation

[soham30rane]

Fixes #481

This will allow the generate_changelog.yml to also do the following

• Fetch latest stable release (this is done explicitly because the currently generated changelog might be for different release than the latest one)
• Update version and release date in conf/config.yaml

[kwankyu]

@haraldschilly In fae9b54, I changed releasedate to release_date. Hopefully, this change does not affect your workflow.

[soham30rane]

I ran autopep8 on the entire file to ensure good formatting. This may result in unrelated formatting changes showing up in the diff, but no functional changes were made beyond the intended scope of the PR

[kwankyu]

LGTM.

[kwankyu]

Thanks!

[haraldschilly]

@haraldschilly In fae9b54, I changed releasedate to release_date. Hopefully, this change does not affect your workflow.

Thx for the heads up, but as long as you also fix the template variables, everything is fine 🌈