- optional `prefix` argument for `add_plugin.py`
- rules directory instead of `rules.rs`
- pathlib syntax
- fix test case where code was added instead of name
Example:
```
python scripts/add_plugin.py --url https://pypi.org/project/example/1.0.0/ example --prefix EXA
python scripts/add_rule.py --name SecondRule --code EXA002 --linter example
python scripts/add_rule.py --name FirstRule --code EXA001 --linter example
python scripts/add_rule.py --name ThirdRule --code EXA003 --linter example
```
Note that it breaks compatibility with 'old style' plugins (generation works fine, but namespaces need to be changed):
```
python scripts/add_rule.py --name DoTheThing --code PLC999 --linter pylint
```