skipMany1 is an Attoparsec combinator that applies a parser at least once, then discards every parsed result. It is useful when input must contain one or more matching characters but their values are irrelevant. section 12.2.2
Require and discard whitespace
Define a whitespace parser that returns (), then require at least one occurrence: `whitespace = void (C8.satisfy isWhitespace)` and `whitespaces = skipMany1 whitespace`. A PNM header can use `whitespace` where exactly one separator is required and `whitespaces` where one or more separators must occur.
