Update everything to work with alpha2

[Gankra]

Collections got renamed, traits got changed, markers changed, coherence changed.

This is basically the "minimum viable product" to get us compiling under alpha2. Doesn't work yet because our dependencies are busted.

I'm totally not clear on the appropriate fix to do to ParVec. I just tossed in a 'static, but the comment in there about static is pretty scary.

[Gankra]

Actually correction: this builds, but our dev dependencies are busted.

[Gankra]

Double correction: I just needed to cargo update.

[Gankra]

Sweet, this cargo tests on my random master snapshot from last night.

[Gankra]

r? @apasel422

The only thing dubious about this is the ParVec change, which I believe can only potentially make the collection useless in some situations, and not actually do anything bad. Seems like an acceptable hack so that we can fix land this and start fixing everything else.

[apasel422]

r+ This looks good overall, in terms of getting things building. The ParVec change seems fine for now.

However, I would like to remove the type parameter from Natural. Multidispatch works, and while it may make inference fail sometimes, it more accurately models the situation and allows us to avoid the ugliness of natural() and PhantomData. Along the same lines, I think it might be possible to simplify the Borrow comparator using multidispatch as well. I can make these changes later, once I've had a chance to experiment with the alpha myself. In order to convert both of these, I think the CompareExt trait needs to change, but I have some ideas for how to support this and will begin investigating.

[Gankra]

Landing as good enough for now. Will iterate in the future.