It's hard to track 2-space indent levels across large vertical gaps, and
it can be hard to suppress the instinct to read the dump as if it were
preorder. This change introduces a new dump mode that addresses both
problems by using box-drawing characters to explicitly represent the
parent-child edges of the tree. This new mode is the default, but the
old behavior remains available with
`--parse-dump-format=yaml-postorder`.
This refactors the diagnostic kind coverage check into something that
also works for node kinds. Then, since this points out a few node kinds
that aren't having their parse verified, I'm adding minor tests for
those.
Geoff Romer
Jon Ross-Perkins