Much of this code is adapted from an earlier experiment. Relative to my old
experiment, I am now distinguishing "green" and "red" trees in the style of
Roslyn, where the latter instrument the former with global positioning
information via a line map. For me a "green tree" is a syntax tree, and a "red
tree" is a cursor.

I am also starting to hook up the tokenisation and parsing into the llbuild2fx
action graph.