Utility function to transform any event stream into a token stream.
template <typename TEvents>
TempEvents<D,Token,/*unspecified*/> Tokenize(TEvents&& source)Emits a token for any event that passes source.
Equivalent to Transform(source, Tokenizer()) with
struct Tokenizer
{
template <typename T>
Token operator()(const T&) const { return Token::value; }
};