add type annotations and args to docstrings

[danielfromearth]

Github Issue: #114

Description

This adds type annotations throughout podaac.merger, especially to clarify the usage of pathlib.Path instead of str for file paths. It's not complete in adding all annotations, but brings up the level of annotations quite a bit.

Overview of verification done

n/a

Overview of integration done

n/a

PR checklist:

• [x] Linted
• [n/a] Updated unit tests
• [x] Updated changelog
• [n/a] Integration testing

See Pull Request Review Checklist for pointers on reviewing this pull request

[jamesfwood]

Hi @danielfromearth Is this ready to go? Can you add us as reviewers? looks great tho btw!