code: func (r *reader) inc() {
  	if r.s[r.p.Offset] == '\n' {
  		r.p.Line++
  		r.p.Col = 0
  	}
  	r.p.Offset += r.w
  	r.p.Col++
  }
docs: // inc increase the position offset of the reader.
  // peek must be called before calling inc!