Add guard page on stack

[npmccallum]

It would be really great if we could come up with some way to allocate a guard page on the stack without a hard dependency on system APIs. For example, on *nix systems we have mprotect(). But in other contexts we need other things. In a kernel context, there will be some internal API that will be used. So this methodology needs to be pluggable.

This also raises the question of the wisdom of passing the stack as a slice. Hopefully, someone will review and comment on that.

[npmccallum]

We can implement this later without much difficulty. Removing from the current milestone.