`decimal`, `hexadecimal`, and `octal` parsers should consume trailing whitespace

Since these are lexemes (at least, they _should be_), they should behave like lexemes: consume trailing white space (but not leading). Currently they don't do it and I find it confusing. If you care to fix it, be careful, definitions of these parsers are used to define other things, so it's easy to introduce new bugs if you're not careful.

Descriptions of these parsers carefully don't call them lexemes, but this is not enough. If you want to preserve current behavior you should explicitly state that these are not lexemes and they do not consume trailing whitespace unlike all other members of `GenTokenParser`.