Add FfM (Fachschaft für Mathematik) synchronizer

This commit moves exceptions and some other things into utils.py and
renames files according to python's file naming guides (kinda).

It also adds a new example config using the new FfM downloader.

PFERD/utils.py

@@ -0,0 +1,29 @@
+import os
+
+__all__ = [
+	"get_base_dir",
+	"stream_to_path",
+	"OutOfTriesException",
+	"UnknownFileTypeException",
+	"FileNotFoundException",
+]
+
+def get_base_dir(script_file):
+	return os.path.dirname(os.path.abspath(script_file))
+
+async def stream_to_path(resp, to_path, chunk_size=1024**2):
+	with open(to_path, 'wb') as fd:
+		while True:
+			chunk = await resp.content.read(chunk_size)
+			if not chunk:
+				break
+			fd.write(chunk)
+
+class OutOfTriesException(Exception):
+	pass
+
+class UnknownFileTypeException(Exception):
+	pass
+
+class FileNotFoundException(Exception):
+	pass