Add new function `getStackArray` to convert a valid eCash OP_RETURN outputScript to an array of data pushes.
`
consumeNextPush` and `consume` are available for more customized processing (e.g. `alias-server` uses the `returnedWith` pushdata from `consumeNextData` to validate for minimum pushes).
`getStackArray` is a simple and common use case.
Also validating for max OP_RETURN size since this is a difficult param for devs to find if they are not intimately familiar with the eCash codebase.