Update memory mod.rs to include missing mod statement on Windows

[JohnDoneth]

Closes wasmerio/wasmer-rust-example#3

Fixes the missing mod statement that exists in the Unix variant of this file. Currently it's blocking any building on Windows.

[CryZe]

This doesn't fix building on Windows though. The memory module itself has a ton of errors and once that builds there's even more in the clif-backend.

[JohnDoneth]

@CryZe Ah, my apologies, I should have checked.

[CryZe]

It seems a lot of new people that came here from the blog post ran into this though. So maybe we could all band together with the guys in #51 to make Windows support happen.

[xmclark]

Windows support is crucial for adoption! Expect to see more progress on #51 soon!

[lachlansneff]

To expand on @xmclark comment, Windows support is very important to us! There's quite a bit of work to do before it can work, however. I'll lay it out here:

1. Get sys::Memory working in Windows.
2. Add signal catching support for Windows. Currently, we use sigaction, setjmp, and longjmp for this.
3. Fix any build/linking issues. We recently made a big leap with that by removing the libffi dependency, but there may be additional work to do here.

[lachlansneff]

We've just gotten windows support working, so this has been solved. It's currently in a pr, but we expect window support to be available in the 0.2.0 release.

[CryZe]

Nice, I'll give it a try tomorrow :D