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.
Strings may not contain a double quote unless it is escaped.
Reference:
https://doc.rust-lang.org/reference/tokens.html#string-literals
(This will still not colorize multi-line strings with an unescaped
newline, will still colorize "this\" as if it were a valid string,
and will still miscolor things when there is another string after
the closing quote of a two-line string. But those things can't
be helped -- line-based regexes cannot emulate a full parser.)
This fixes https://savannah.gnu.org/bugs/?61361.
Reported-by: Elias Jonsson <e@ejon.eu>
Bug existed since version 2.6.1, since the Rust syntax was introduced.
Benno Schulenberg