Add gen-packages and package-dir configurations

[LeboyX]

The 'gen-packages' configuration is a boolean config that controls the command's recursive scan of grammar-package directories. When set to false ("no"), the tool won't add init.py files to any directories other than the grammar parsers' directory.

The 'package-dir' flag tells control what is considered the "base_dir" for the creation of init.py files. The base_dir is excluded from the creation of init.py files.

[LeboyX]

Build seems to've failed due to a...version conflict(?!) for pytest, or its dependency pytest_cov. Looks like it needs a version >= 3.6, but the build only got 3.3.0. I don't think my changes could've influenced this, so I'm a little perplexed.

[coveralls]

Pull Request Test Coverage Report for Build 97

• 14 of 14 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 96:	0.0%
Covered Lines:	261
Relevant Lines:	261

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💛 - Coveralls

[ferraith]

Thank you very much for your PR. I decided to completely remove this weird init file generation.