After weighing up the options it seems that Golang's termbox-go TTY
library has better support for terminals, and it's cross-platform out of
the box. So this commit is the first working version where the
interfacer launches a websocket server, makes a connection to the
webextension and listens to STDIN from the CLI, sending all input to the
webextenstion.
This proves that frames can be generated on Firefox using the canvas and
a Tree Walker to examine text nodes. Already with little optimisation
frames don't ever take longer than 200ms to render.
Chrome has a MediaStream of the viewport, hopefully that will prove
performant as well.
This doesn't have functioning text colour detection or text occlusion
support. But early research suggests this will possible by comparing 2
screenshots: one with and the other without rendered text.
