config: allow spreading config over multiple files

This commit enables spreading the config in /etc/sr.ht - and, crucially,
_only_ in /etc/sr.ht - over multiple .ini files.

As before, if a file ./config.ini is found, it (and only it) is loaded
and any config in /etc is ignored.

Spreading the config over multiple files will make it much easier to
create containerized versions, where e.g. different secrets can be made
available in different files, but rendering it all into one big file
would require some preprocessing.

srht/config.py

@@ -1,3 +1,4 @@
+from glob import glob
 from urllib.parse import urlparse
 from configparser import ConfigParser
 from werkzeug.local import LocalProxy
@@ -11,17 +12,23 @@ _config = None
 
 config = LocalProxy(lambda: _config)
 
+def load_one(path):
+    try:
+        with open(path) as f:
+            _config.read_file(f)
+        return True
+    except FileNotFoundError:
+        return False
+
 def load_config():
     global _config
     _config = ConfigParser()
-    paths = ["config.ini", "/etc/sr.ht/config.ini"]
+    # Loads _either_ config.ini _or_ all .ini files in /etc/sr.ht
+    paths = ["config.ini", "/etc/sr.ht/*.ini"]
     for path in paths:
-        try:
-            with open(path) as f:
-                _config.read_file(f)
+        loaded = any(map(lambda p: load_one(p), glob(path)))
+        if loaded:
             break
-        except FileNotFoundError:
-            pass
 
 load_config()