support of user-created components, using pathlib, and renaming part filename

[tingjhenjiang]

1. now users can retrieve components they created on their own.
2. using pathlib in path generation and file writing for more robustness in different env.
3. if there are slashes or backslashes in the part name/component name, writing files would cause errors. Now correct it.

[uPesy]

@tingjhenjiang Thanks a lot for your contributions. Before merging your code, could you :

• target the dev branch instead of master
• split the PR in 3 for each new features
• The code should work with python 3.9 since the builtin python in Kicad 6/7 is python 3.9.14