Add Format-Coverage -PesterResults

[dahlbyk]

Following on from dahlbyk/posh-git#461, it would be nice if PR builds could report coverage in their build log even if it's not pushed to Coveralls. That's not currently possible because the Format-Coverage call requires -CoverallsApiToken.

My proposal is pretty simple: add a second parameter set that accepts an existing set of Pester results.

[JanDeDobbeleer]

This one was on my list as well, I just added these lines to validate whether or not the provided results contain the CodeCoverage object

if (!$PesterResults.CodeCoverage) {
    Write-Error 'Please provide pester results with code coverage using the -CodeCoverage parameter'
    exit 1;
}

Would you mind if I add them to your commit and merge it like that? Other than that, everything seems in tiptop shape.

Also, funny how a module about code coverage has 0 tests (I'll have to fix that).

[dahlbyk]

Opted for return here since Write-Error can be made fatal by setting $ErrorActionPreference = 'Stop'. Thoughts?

[JanDeDobbeleer]

I agree. This leaves all options open. I'll merge this little baby.

[JanDeDobbeleer]

Rebased and merged. Thanks for contributing!