* load application from factory function
Use `ast.parse` to validate that the string passed to the CLI is either
an attribute name or a function call. Use `ast.literal_eval` to parse
any positional and keyword arguments to the function. Call the function
to get the real application.
Co-authored-by: Connor Brinton <connor.brinton@gmail.com>
* test coverage for util.import_app
* document app factory pattern
