More descriptive names of test files

[narimiran]

As noted here:

Note that tissues.nim, tmisc.nim are not unique names and considering testament runs things in parallel, it is hard to tell from the logs which instance actually failed. You might want to include the category name in the filename for clarity.

[Araq]

I love your work.

[timotheecour]

@narimiran

it is hard to tell from the logs which instance actually failed

can we make testament print relative path of files being tested, eg:
instead of printing
foo.nim
print:
tests/concepts/foo.nim
(or at least: concepts/foo.nim but I prefer strongly the former)