Tweaks to the codepaths related to the cross version IG pre-processor

[brianpos]

Specifically:

• remove the hard-coded path to /Users/grahamegrieve/work/fhir-cross-version and pass the path via parameters
• ensure the temp/xver-qa path exists before trying to read/write to it

[grahamegrieve]

I think we want to get rid of all those saving files that have hardcoded file paths

[brianpos]

I think we want to get rid of all those saving files that have hardcoded file paths

@grahamegrieve I agree with that, but do need the other change here with the checking that the temp/xver-qa path exists...
(that's what's killing the package CI build at the moment)
Would you like a seperate PR with just that change in it?