Refactor plugins and main module

[yammesicka]

• Sort imports
• Use pathlib
• Move the package listing to package.__all__
• Use absolute rather than relative imports
• Refactor functions structure
• Use dictionary unpacking on plugin parameters
• Catch IOError when trying to read config
• Use fstrings instead of str.format(dict)
• Format docstrings according to PEP 257
• Make all the code use ' instead of "
• Use platform library instead of _platform