Implement completion window as non-modal

The new autocompletion is quite awesome, but it's distracting to see a new modal window pop up for completion. It's great that it's always there, but the visual style of the window feels so heavy handed - the focus is lost from Vico. Sublime and Vim's autocompletion appears to be embedded int the document which has a much nicer ambient feel. Change your mac os's three circle buttons to be red[close]/green/yellow (instead of the gray theme) to really see the effects of a modal window - the colors of the window's close button changes as you type!