Lexer: patterns that start with '^' match not only from beginning of the string

[darvin]

Lexer: patterns that start with '^' match not only from beginning of the string - that's different from flex behaviour

[GerHobbelt]

See also #67: given the way that the Jison lexer works, /^/ represents the start of the rest of the input which still needs to be lexed.

%options flex doesn't solve this issue; the work-around posted in #67 might work though (I never tested it as I've never had a need for this semantic meaning of /^.../