sublime: Replace the f-string macro with a Python plugin.

Macro approach is less reliable because the path to the macro
file has to be hardcoded.  If MP is installed into a non-standard
dir, the {} completion wouldn't work properly.

Author: 1st1

settings/sublime/Default.sublime-keymap

@@ -31,9 +31,8 @@
             { "key": "selector", "operator": "equal", "operand": "string.quoted", "match_all": true }
         ]
     },
-    // Replace a '{|}' with '{{|' when typing within fstring
-    { "keys": ["{"], "command": "run_macro_file",
-    "args": {"file": "Packages/MagicPython/settings/sublime/fstring_brace.sublime-macro"},
+    // Replace a '{|}' with '{{|' when typing within f-string
+    { "keys": ["{"], "command": "fstringbrace",
     "context":
         [
             { "key": "setting.auto_match_enabled", "operator": "equal", "operand": true },

settings/sublime/fstring_brace.sublime-macro

@@ -0,0 +1,18 @@
+"""A plugin for Sublime Text to enhance f-string editing experience.
+
+Specifically, this plugin simplifies typing of escaped curly braces
+in an f-string:
+   {|}, where | is for cursir, gets replaced with
+   {{|, when '{' is typed again.
+"""
+
+
+import sublime
+import sublime_plugin
+
+
+class FstringbraceCommand(sublime_plugin.WindowCommand):
+    def run(self):
+        view = self.window.active_view()
+        view.run_command('right_delete')
+        view.run_command('insert', {'characters': '{'})