Provide a command to open standard goto-anything menu if nothing is selected

[MatmaRex]

Let's provide a command to open standard goto-anything menu if nothing is selected. This would make it possible to seamlessly replace the standard menu with the one provided by this package. (It should probably not be bound to any hotkey by default, just documented as existing.)

It can be trivially implemented using something like below, but such copy-pasting looks like an ugly solution, and my Python is too rusty for something prettier.

class GotoSelectionIfAnyCommand(sublime_plugin.WindowCommand):
    def run(self):
        for region in self.window.active_view().sel():
            if region.empty():
                lineContents = "";
            else:
                lineContents = self.window.active_view().substr(region)

        if len(lineContents) > 0:
            while (lineContents[0] in "# "):
                lineContents = lineContents[1:]

        self.window.run_command("show_overlay", {"overlay": "goto", "text": lineContents + "!", "show_files": "true"})
        self.window.run_command("left_delete")

(Note that this is using the hack I proposed in pull request #2.)