Better test case

[ralfbiedert]

I improved the test case a bit:

• Code style should be more in line with your existing code
• Tried to cover all primitive types (u8 ... f64)
• Removed the uneven test
• Renamed test from zip to kernel, as it more reflects what the test does.

@AdamNiederer, please let me know if you want these tests to be named / work differently. I shamelessly implemented what I need to be verified for my own project, and I assumed tests in the individual source files are unit tests, while those under tests/ are more "integration" tests (e.g., building a SIMD kernel).

[AdamNiederer]

@AdamNiederer, please let me know if you want these tests to be named / work differently. I shamelessly implemented what I need to be verified for my own project, and I assumed tests in the individual source files are unit tests, while those under tests/ are more "integration" tests (e.g., building a SIMD kernel).

I'll probably add a few more myopic tests to iters.rs once I stabilize the explicit API, but those look sufficiently "big-picture" for their own module. Thanks for fixing the docs, as well :).