Refactor configuration file parsing

Now the time for importing the kitty.config module has been halved, from
16ms from 32ms on my machine. Also, the new architecture will eventually
allow for auto generating a bunch of python-to-C boilerplate code.

kitty_tests/__init__.py

@@ -6,11 +6,12 @@ import os
 from unittest import TestCase
 
 from kitty.config import (
-    Options, defaults, finalize_keys, finalize_mouse_mappings, merge_configs
+    Options, defaults, finalize_keys, finalize_mouse_mappings
 )
 from kitty.fast_data_types import (
     Cursor, HistoryBuf, LineBuf, Screen, set_options
 )
+from kitty.options.parse import merge_result_dicts
 from kitty.types import MouseEvent
 
 
@@ -106,7 +107,7 @@ class BaseTest(TestCase):
         final_options = {'scrollback_pager_history_size': 1024, 'click_interval': 0.5}
         if options:
             final_options.update(options)
-        options = Options(merge_configs(defaults._asdict(), final_options))
+        options = Options(merge_result_dicts(defaults._asdict(), final_options))
         finalize_keys(options)
         finalize_mouse_mappings(options)
         set_options(options)