Experimental ex-mode support for vim-mode-plus

My thought about providing ex or command(:) in Atom is here #52.
I still not much motivated for this package.
So fixing, enhancing this vim-mode-plus-ex-mode package is tend to be delayed.
So please understand this package as reference, example, prototype implementation.
Don't ask me to improve this package into true ex-mode emulation.

There is no default keymap.

'atom-text-editor.vim-mode-plus.normal-mode':
  ':': 'vim-mode-plus-ex-mode:open'
  '!': 'vim-mode-plus-ex-mode:toggle-setting'

• 11: Move to line 11
• 50%: Move to 50% of buffer.
• 15:10: Move to column 10 of line 15
• !: Toggle boolean config parameter
• w, wq, split, vsplit etc.