in *parse_impl(); add support to the error handlers and their support
functions directly instead. There are simply too many APIs there that need
the translation to leave it to other code.
Add lex_error exception type, and add support for all the APIs that used to
take a parse_error param to now take either a parse_error or a lex_error.
Throw lex_error from failed parsing of lexed tokens in detail::make_token().
See #202.