nimble test keeps git status clean; prevents accidental checking in of binaries etc

[timotheecour]

• git status should always be clean when running tests. after this PR (say, from a fresh nimble clone), nimble test should keep git status clean
• this prevents accidental checking in of binaries etc
• speaking of which, I git rm tests/nimbleVersionDefine/src/nimbleVersionDefine in this PR
• try as much as possible to build test artifacts under a single dir (can be improved in future PR's)
• simplify & more robust/DRY gitignore logic in particular for genarated nims binaries and binaries without extensions

[dom96]

I applaud your fight to keep git status clean, I think your proposal in that issue you wrote has more merit.

[timotheecour]

@dom96 friendly ping

[dom96]

hm, alright, seems good. Can you rebase?

[timotheecour]

PTAL
sadly, CI was green before rebase, but since nimble's CI is red, this PR's CI is now also red

[dom96]

Yeah, dunno what's going on with the CI. I created iffy/install-nim#8

[timotheecour]

@dom96 PTAL, finally green

[dom96]

thanks!