feat(config): walk file hierarchy for project config (#1475)

The current naïve implementation of attempting to load configuration
from the current working directory is insufficient for having
project-wide selection of checks. Here, we traverse the file tree up
from the current working directory in search of configuration files,
enabling proselint to find them at the project root.

Author: Nytelife26

proselint/config/paths.py

@@ -1,6 +1,7 @@
 """Configuration paths for proselint."""
 
 import os
+from itertools import repeat
 from pathlib import Path
 
 XDG_CONFIG_VAR = "XDG_CONFIG_HOME"
@@ -21,5 +22,6 @@ def _get_xdg_path(env_var: str, default: Path) -> Path:
 
 config_paths = [
     cwd / "proselint.json",
+    *map(Path.__truediv__, cwd.parents, repeat("proselint.json")),
     config_user_path / "proselint" / "config.json",
 ]