feat: Allow to pass entry point to clipstick parse function#57

This is helpful, when list of CLI args comes not from `sys.argv` and, as result, entry point cannot be parsed from `sys.argv[0]`. This is also might be helpful for cases, when some CLI called via `python3 -m ...` and `sys.argv[0]` as result contain meaningless value of `something/__main__.py` (however, looks like, the proper fix for that case is out of scope of current change). **ps.** Thanks a lot for `clipstick` library 🙏 Very appreciate your work, as it makes my life much more easier 🙇