improve match explanations

improve match explanations

Using == and != proved too hard to read, so went with [TRUE] and [FALSE]
after the term. I would kind of liked to have used emojis for a green
check and red X, but probably that is too fancy to be a good idea.

Make --explain output be inside [ ] with whitespace around them, to
avoid it ending with eg "[FALSE]]" and to make it easier to visually
find the start of it.

Sponsored-by: Dartmouth College's DANDI project