fs: add minimal module to get some directories

bebop/fs.py

@@ -0,0 +1,18 @@
+"""Retrieve some paths from filesystem.
+
+A lot of logic comes from `appdirs`:
+https://github.com/ActiveState/appdirs/blob/master/appdirs.py
+"""
+
+from os import getenv
+from os.path import expanduser, join
+
+
+APP_NAME = "bebop"
+
+
+def get_user_data_dir():
+    """Return the user data directory."""
+    path = getenv("XDG_DATA_HOME", expanduser("~/.local/share"))
+    path = join(path, APP_NAME)
+    return path