fix: allow relative paths for outDir and staticDir

[csvn]

This PR consists of several commits, where the goal is to re-enable the test (fix for Windows), as well as allow relative paths for config options to address #2913.

1. Re-enables test and normalizes paths for Windows
2. Add unit test for normalizeConfig and the root option
3. Add unit test for normalizeConfig for build.outDir and staticDir, and allow the properties to be relative
4. Add JSDoc for fields in FreshConfig

I can split these into separate PR's if preferred, but all code changes are very in nearly the same places.

Closes #2913

[marvinhagemeister]

Sweet, thanks!