Begin a basic test suite via cram

This adds a partial cram test suite mostly covering mkrc, lsrc, and rcrc.

https://bitheap.org/cram/

It can be run like so:

```
$ SRC="$PWD" cram ./test
```

Or

```
$ SRC="$PWD" cram ./test/some-test.t
```

It seems mkrc and rcup are returning an exit status of 1 when there are no
after hooks to be run. The test suite was added with the aim of not touching
any implementation code, so they assert this behavior now and will need
updating once that's fixed.

I've not added any documentation since this is a bit of a spike and developers
need not know it's here just yet.