Couple of additional tests for clarity

[mikejcurry]

As part of looking at typelevel/simulacrum#49 I wanted to find out a bit more about the imp macro.

In particular, I wanted to prove to myself that using macro summon for apply was better than using imp[A] for the apply implementation.

I was close to 100% confident on that anyway, but I wrote a couple of tests to make sure.

As part of doing that, I found the tests that had already been written very instructive, in the way that they tell a story by creating a baseline for comparison in a couple of the tests and then using that as a base to draw conclusions in the other tests.

I updated the descriptions of the tests to tell this story using the test descriptions in a more english language way, and also included the two extra tests I'd added for myself.

I thought this would be worth submitting as I certainly found the whole thing instructive and educational and I am hoping that these changes may also make the tests useful for others.

[non]

Hi @mikejcurry sorry I missed this! Thanks, these are great!