Allow sequence of strings or Path objects for allow_paths

[iamdefinitelyahuman]

Overview

Currently, allow_paths must be given as a comma-separated string. It would be easier to use and more intuitive if this kwarg instead expected a sequence of either strings or Path objects.

Specification

1. In main.compile_source, main.compile_files, and main.compile_standard, expect allow_paths to be given as a sequence of strings or Path objects.
2. Add test cases. Consider the following:
   • PosixPath and WindowsPath
   • absolute and relative paths

Dependencies

#53