Update tests.
Reason: it turns out that the native output generated by
pretty-simple isn't always readable by the native reader.
According to https://github.com/cdepillabout/pretty-simple/issues/99
it is not a design goal of the library that the rendered values
be readable using 'read'. This makes it unsuitable for our
purposes.
pretty-show is a bit slower and it uses 4-space indents
(non-configurable), but it doesn't have this serious drawback.
Previously we used our own homespun formatting. But this
produces over-long lines that aren't ideal for diffs in tests.
Easier to use something off-the-shelf and standard.
Closes#7580.
Performance is slower by about a factor of 10, but this isn't
really a problem because native isn't suitable as a serialization
format. (For serialization you should use json, because the reader
is so much faster than native.)
We previously indented them by two spaces, following a
common convention. Since the convention is fading, and
the indentation is inconvenient for copy/paste, we are
discontinuing this practice.
Closes#5440.
Emacs always uses two spaces when indenting the content of src blocks,
e.g., when exiting a `C-c '` edit-buffer. Pandoc used to indent contents
by the space-equivalent of one tab, but now always uses two spaces, too.
Closes: #5440
