Include a utility script to change GEOS-Chem Classic version numbers before release

[yantosca]

Name and Institution (Required)

Name: Bob Yantosca Institution: Harvard + GCST

Confirm you have reviewed the following documentation

• [x] Contributing guidelines

Describe the update

This PR adds a script that changes the GEOS-Chem Classic version numbers in the following files:

• CMakeLists.txt
• docs/source/conf.py
• CHANGELOG.md
• src/GEOS-Chem/CHANGELOG.md

This is a convenience script for use by the GCST before new versions are released.

Expected changes

This is a no-diff update.

Related Github Issue(s)

• https://github.com/geoschem/HEMCO/pull/242
• https://github.com/geoschem/GCHP/pull/357

[yantosca]

This pull request looks good to merge.

Note that for the script to properly update CHANGELOG.md, that file will need to utilize [Unreleased] - TBD as the version header.

Actually the regexp will work as long as it finds Unreleased in brackets. So it should succesfully update:

[Unreleased]
[Unreleased X.Y.Z]
[Unreleased] - TBD
[Unreleased X.Y.Z] - TBD