ENH: add token::read(Istream&) method

- can be used to simplify some logic. For example,

      if
      (
          (tok.read(is) && tok.isWord("FoamFile"))
       && (tok.read(is) && tok.isPunctuation(token::BEGIN_BLOCK))
      )
      ...
  vs
      if
      (
          (is.good() && (is >> tok) && tok.isWord("FoamFile")) ...
       && (is.good() && (is >> tok) && tok.isPunctuation(token::BEGIN_BLOCK))
      ) ...