Recursive directory parsing + ignore common YAML dirs we shouldn't check

[nonprofittechy]

• Running dayamlchecker . now works the same as black . and mypy ., gathering checkable files as it runs in subdirectories
• This immediately raises a bunch of false positive failures when you run in a package root. We could add some "is this a Docassemble YAML?" heuristic, but for now just going to ignore the most common ignorable directories, /sources/ and .github

[BryceStevenWilley]

A lot of comments, but really only two suggestions:

• change include_default_ignore to check_all, a clearer name
• add .venv to the ignored dirs.