g++ 4.8.2 compile errors

[HJiahu]

i could not compile this project with g++ 4.8.2, the error is :

flex_lexer.l:249:36: error: use of deleted function 'std::basic_stringstream& std::basic_stringstream::operator=(const std::basic_stringstream&)'

my solution :
modify the line of 249 in flex_lexer.l from \' { BEGIN singlequotedstring; strbuf = std::stringstream{}; } to
\' { BEGIN singlequotedstring; strbuf.clear(); strbuf.str(""); }

[mrks]

Thanks for the suggestion. I'll open up a PR in a second.