[REF] Reformat rapidtide parser and usage documentation

[tsalo]

Closes None. I should have opened an issue about this before opening this PR, but I wanted exhibit some changes I was hoping to make to the package with a test case (the rapidtide parser).

Changes proposed in this pull request:

• Run black on workflows/rapidtide_parser.py and workflows/parser_funcs.py. This standardizes the style a bit and should help with PEP8-related issues. Plus, it has the added benefit of minimizing future diffs, which will make it easier to review changes.
• Switch from printing messages to logging them in workflows/rapidtide_parser.py (related to Switch from printing to logging messages #41).
• Add some argument group-level descriptions (in addition to the titles) in workflows/rapidtide_parser.py.
• Adopt UpperCamelCase for a class in workflows/parser_funcs.py, to match PEP8 convention.
• Adopt CAPITALCASE for constants in workflows/parser_funcs.py, to match PEP8 convention.
• Clean up a few heading levels in docs/usage.rst, and add a comment that documents the levels for easy reference (I kept confusing myself).
• Use code formatting in a couple of places in docs/usage.rst, which might make referencing arguments a little easier.
• Hide debugging-related arguments in the argparse-generated documentation in docs/usage.rst. I didn't actually know about this feature before now, and it's pretty cool!

[tsalo]

Based on the pattern of changes you saw in this PR, how do you feel about running an automated code formatter like black on rapidtide? I was thinking that it might be good to run right before you do the official 2.0.0 release.

[bbfrederick]

All for it. Especially if it will shut PyCharm up about PEP8 violations.

[tsalo]

Awesome! I'll open an issue, and it can wait until just prior to the official release of 2.0.0.