Added new features, fixed bugs, and smoothed rough edges.
===== New features:
1.  ,, in normal mode now moves to insert mode.  Convenient: ,, in insert mode does nothing, unless there is an abbreviation template available.
2. <esc> in normal mode works like Ctrl-G.
===== Fixed bugs
- Fixed crashers in vc.on_same_line
- h and l command now woks in visual mode in headlines.
- vc.on_idle calls vc.set_border only for the presently selected .leo file. Without this check, there are problems editing headlines.
===== Smoothed rough edges
- vc.do_key now delegates all keys if not vc.is_text_widget(vc.w)
  This should eliminate the need for vc.vim_arrow and tests against vc.is_text_widget.