users can pass additional_hooks_dir to pyinstaller

[NileGraddis]

For many popular packages the hooks included with pyinstaller are sufficient, but for less prominent (or non-public) packages, custom hooks are required.

This PR allows users to specify additional directories for pyinstaller hooks in their settings files. This looks like:

{
...
    "additional_hooks_dir": ["some_hooks", "some_more_hooks"]
...
}

and causes pyinstaller to look for hooks in all listed directories in addition to fbs/freeze/hooks.

Thank you for making fbs! Please let me know if this is the right approach to take. If so, I will go ahead and add a test.

[claassistantio]

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[mherrmann]

Thank you very much for the PR. I'm happy to hear that you like fbs.

Your PR is similar to other requests I get sometimes. Namely, that people want to be able to pass additional command line parameters to PyInstaller. Another example of this is for instance #149.

So far, my stance on this has been to not expose PyInstaller-specific settings as part of fbs's API. The reason is that once I do this, I am forever tied to not just PyInstaller, but also to its very specific settings (which might change across PyInstaller versions).

Your request makes me think whether I shouldn't just sometime add one fbs setting, extra_pyinstaller_args. It would be very similar to this PR, except people would write

{
    "extra_pyinstaller_args": [
        "--additional-hooks-dir", "some_hooks",
        "--additional-hooks-dir", "some_more_hooks",
    ]
}

instead of your snippet. But as I said, this would (kind of) tie me (/fbs) forever to PyInstaller.

[mherrmann]

(Oh and see #149 for the currently recommended way of doing what you want to achieve.)

[mherrmann]

Implemented via extra_pyinstaller_args as described above in fbs release 0.8.9. Thanks!