Primarily {h,j,k,l,left,right,up,down} for moving to a pane by
direction; but also {w,W,p} for going forward/back, and {v,s} for
splitting a pane vertically/horizontally, and {c,q} to close a pane.

There are a large number of ctrl-w commands that are not supported, and
which fall into three buckets:

* switch this pane with that one (VScode also has this, and it's a
  requested feature)
* move to top/bottom/leftmost/rightmost
* counts on any of these
* jump to "definition/file-under-cursor/etc.etc." in a new pane.