Throw from action gets confusing error

[diyessi]

If an action throws, for example because an any_cast has the wrong type, the problem typically (for me, at least) shows up in the ~Context at assert(cut_stack.empty());, which can be very confusing until you realize what is really going on.

[curldivergence]

Btw the same problem was mentioned in #269, for now I’ve just commented out that assertion from cpp-peglib.

[yhirose]

@diyessi, @curldivergence could you try the latest peglib.h? Hope it fixes the issue.