Underlines in names are not parsed!

[fklemme]

Using a parser like ((qi::alpha | '_') >> *(qi::alnum | '_')) will not drop underlines in function and variable names! The implicit qi::lit('_') has no attribute. qi::string("_") has to be used instead. See http://www.boost.org/doc/libs/1_62_0/libs/spirit/doc/html/spirit/qi/reference/string/string.html.

This is wrong in instruction_grammar.h and expression_grammar.h.