This introduces some fancy macro action that allows us to skip the four calls to `(concat-spec …)` with the different generators and types.
@ErikRauer and I wrestled with this for a _long_ time today, and it turned out that it was absolutely necessary to quote the generators in `gen-type-pairs on lines 10-13. I'm not 100% sure why, but it seems that without that something (perhaps a level of macro-ness) got unwrapped too early and then it couldn't find the generator because it had lost the namespace it belonged in.
Whether this actually _simplifies_ things is really up for debate. If this is as far as we get, it's probably not worth it. If we can find a reasonable way to reduce the other sources of duplication, however, it might be worth it?
This adds test.check tests for `vector/_last`. This is _really_ similar to `vector/_first` (and the other vector tests), so I think there are definitely ways to extract common logic from these.
This is a start on using `test.check` to write tests for the vector instructions. We currently have tests for:
* `vector/_emptyvector`
* `vector/_indexof`
* `vector/_subvec`
There are _lots_ of other functions still to be tested.
This did reveal errors in `vector/_subvec`, which will be addressed in the next commit.
We used macros to make it easy to generate tests for each of the four vector types; this should be extensible to additional vector types in the future if needed.
