Substitution now calls vc.done/vc.quit if c.vim_mode is True.  This allows makes :s work properly even when not in vim mode.

Leo build: 20140822165356
A major reorganization of the vim to-do list, taking into account what has been done, and what no longer needs to be done.
Reorganized Tom L's notes into items that apply to vim-like @mode bindings and Leo's new vim-mode.
There is still a huge number of unfinished features in the vim reference card, but the number of unfinished basic features is dwindling.

Leo build: 20140822165920