allow ascii symbols_parser to be matched against unicode chars

[theodelrieu]

@Kojoley

Following up on #649, I inverted the test based on your comment. Let me know what you think about it!

[Kojoley]

My gut feeling tells me that this will open a can of worms, consider this example: BOOST_TEST((!test(U"\U000001613", no_case[foo])))

[theodelrieu]

@Kojoley True this can lead to weird stuff like your example.

I'd like to avoid that kind of patches, but right now I don't see how to workaround my problem without writing all my grammars in UTF32.

[theodelrieu]

@djowel What do you think about this one?

[djowel]

I can understand @Kojoley's concern. I'm uneasy with it as well, but I do not have an easy solution ATM. Perhaps if you can start with a simple mvce use-case, we can find something that can work better. I'm thinking something explicit, rather than implicit.

[theodelrieu]

Understood, I will try to come up with a MCVE later this month.