feat: accept pathlib in the API

[mxschmitt]

Drive-by standardise the usage of path objects in the project and cleaned up the tests for the __dirname usage.

Lesson learned: if path is a string just wrap it in Path() as usual. It does also work if path is already a Path object.

https://docs.python.org/3/library/pathlib.html

[coveralls]

Pull Request Test Coverage Report for Build 189031475

• 21 of 25 (84.0%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 87.977%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
playwright/main.py	5	9	55.56%

Totals
Change from base Build 188830934:	0.06%
Covered Lines:	3205
Relevant Lines:	3643

---

💛 - Coveralls