This required a little more restructuring of Global_state. It's not flat
now, it's hierarchical again, but in a different way.
after commit 3d89b8eb9d:
post
\- reply A
\- reply B
\- reply C
after commit f9f7dab9b7:
post
reply A
reply B
reply C
after this commit:
row
\- col
\- indent 0
\- post
\- col
\- indent 1
\- reply A
\- col
\- indent 2
\- reply B
\- col
\- indent 1
\- reply C
The indents are just invisible rectangles of different widths with 0
height.
One change I had to make was to initialize_editor. Neither luaML and
driver load lines from disk, but that's arguably the common scenario to
support.