Auto formatting for Python files

[jfredrickson]

Improve pre-commit Python formatting per #213.

This does a few things so far:

• If you're using VS Code or a VS Code based editor, it should recommend the Black Formatter extension upon startup
• Enables format-on-save for Python files using Black
• Updates the pre-commit hook to run Black (which, if you're using VS Code, shouldn't have any changes left to make)

To get this to work:

1. Ensure you have Black Formatter installed (hopefully if you're using VS Code, it'll prompt you to do so if you don't already have it; let me know if it doesn't prompt you)
2. cp pre-commit .husky/pre-commit to make sure Husky has the latest pre-commit configuration

[jfredrickson]

Now with auto stashing. The script now does this:

1. Stashes all unstaged changes
2. Runs the formatters as usual
3. Runs git add . to add any changes from the formatters to the current commit
4. Pops the unstaged changes from the stash

[jfredrickson]

Okay, taking a different angle to this due to conflicts caused by stashing. Copied the simplified hook over from PR #310 and this will only format the code if there are no unstaged changes.