Also, trim some whitespace and group one rule better.
Also, fix a stray closing parenthesis in the JSON syntax,
and add the missing slash to the possible escaped characters.
(Reference: https://www.json.org/json-en.html.)
Also, improve the ending of multiline strings in the Rust syntax.
A forward slash does not need to be escaped, and the backslash itself
should not be escaped: it serves to escape the star, to make it literal.
Also, remove a stray end-of-line anchor ($).
