auto-complete from open buffers (feature suggestion)

[vizcay]

It will be great to have this feature in micro, and it would be language agnostic. Open auto-complete with < Tab > (if the current word partials match don't insert character) or some other shortcut (Ctrl+Space) and use up and down to navigate the suggestion list.

[zyedidia]

Related to #174.

[vizcay]

@zyedidia it's related but that's more like snippets or common patterns for programming languages. The kind of auto-completion I suggest, can be done even writing a letter when a word repeats. Of course, adding plugins to improve the list suggestion will be great, but not entirely necessary for a start.