censor size/offset info for opaque data

[dherman]

Views of TypedBuffers should not expose size or offset information. Several options:

• produce NaN or 0 from the accessors
• throw from the accessors
• don't provide the accessors at all on the views

For backwards compatibility with typed arrays, I think the best option is to throw.

[dherman]

I went with throwing.

https://github.com/dherman/structs.js/commit/66b98dfdebcf7ee26f95a40d1ba6c38fd5e1d9eb