change _fitText to _update
change _fitText to _update

I realized it makes more sense to call the function responsible for
fitting the border and background around the text _update and call it
asynchronously. I've also simplified the process to put space between
multiple lines by adding a _font.spacing attribute. Finally, _dis.context
now permanently tracks it's font attribute so that the proper line width
can be calculated in the _update function.

sedabull/Greenhorn,sedabull/Greenhorn