Document returned result of Tool.main(...) and add result type for main(...)
toolbaseapp.py returns an
int but the docstring does not explain what it means.
Also, each tool defines a global
main() that returns this same
int, but those functions
don't seem to have an explicit result type. Add a result type.
mypy warnings were not heeded.
This does not affect functionality, but it is not the way it should be.