Currently, the docs for Prim say that Int is a 32-bit signed integer. However, in #1094, we seemed to be moving towards a consensus that the number of bits in an Int should be allowed to vary between platforms and backends.

Since there's a bit of confusion regarding this type (e.g. "Why doesn't it go up to Number.MAX_SAFE_INTEGER") I'd like to clarify this. I think the options are:

• Decide that Int really is exactly 32 bits
• Define Int as a twos-complement signed integer with at least 32 bits
• something slightly different from either of these? I'm not sure.

Whatever we decide we should update the Prim docs appropriately.