Improve lexer's error reporting. You get the whole token mentioned now
in parse error messages, not just the part scanned by the last flex rule.
For example,
select "foo" "bar";
used to draw
ERROR: parser: parse error at or near """
which was rather unhelpful. Now it gives
ERROR: parser: parse error at or near ""bar""
Also, error messages concerning bitstring literals and suchlike will
quote the source text at you, not the processed internal form of the literal.