run: rename cryptic tmu to tmux-split, ./run is good now so I never use it anymore explicitly

run

@@ -718,7 +718,7 @@ Extra options to append at the end of the emulator command line.
             if self.env['tmux_args'] is not None:
                 tmux_args += ' {}'.format(self.env['tmux_args'])
             subprocess.Popen([
-                os.path.join(self.env['root_dir'], 'tmu'),
+                os.path.join(self.env['root_dir'], 'tmux-split'),
                 "sleep 2;{} {}".format(tmux_cmd, tmux_args)
             ])
         cmd.extend(extra_emulator_args)

tmux-split

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# TODO: move to Python.
 if [ "$(tmux list-panes | wc -l | cut -d' ' -f1)" -ne 1 ]; then
   tmux kill-pane -t 1
 fi