Banner.{W,H} made pointers, pointer helpers added

Changes since v8.0.0:

• Banner.{W,H} fields made pointers - #16
• {Int8,Uint64}Ptr(n) and ENUM(n).Ptr() helpers added:

Banner {
  W: Uint64Ptr(320),
  H: Uint64Ptr(240),
}

BidResponse {
  NBR: NoBidReasonCodeTechnicalError.Ptr(),
}

Video {
  StartDelay: StartDelay(60).Ptr(),
}