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.

example_config.py

@@ -0,0 +1,29 @@
+import PFERD
+import asyncio
+import logging
+import pathlib
+
+logging.basicConfig(level=logging.INFO, format=PFERD.LOG_FORMAT)
+
+base_dir = PFERD.get_base_dir(__file__)
+
+def hm1(old_path):
+	if old_path.match("blatt*.pdf"):
+		return pathlib.PurePath("Blätter", old_path.name)
+
+	return old_path
+
+def ana1(old_path):
+	if old_path.match("*zettel*.pdf"):
+		return pathlib.PurePath("Blätter", old_path.name)
+
+	return old_path
+
+async def main():
+	ffm = PFERD.FfM(base_dir)
+	await ffm.synchronize("iana2/lehre/hm1info2018w/de", "HM1", transform=hm1)
+	await ffm.synchronize("iana1/lehre/ana12018w/de", "Ana1", transform=ana1)
+	await ffm.close()
+
+if __name__ == "__main__":
+	asyncio.run(main())