[m-rev.] for review: combined higher-order types and insts

[Mark Brown]

On Sun, Jan 31, 2016 at 5:50 PM, Mark Brown <mark at mercurylang.org> wrote:
> Hi,
>
> This implements the new language feature that I proposed recently
> under the heading of subtypes.
>
> Part of the change is that I've moved some code to a new module and
> also modified it. This doesn't show up in a full diff very well, so
> I've also attached the diff of just these modifications to the new
> module.

For now, I've pushed a change to move the code to the new module, but
without any modifications. This is best committed separately to the
main change, and doing it now means it will be less likely that merge
problems arise later.

Mark