config: Add test for Windows local paths.

[filipnavara]

• Make sure that go-git is able to read unquoted local Windows path with escaped characters (as written by cgit).
• Add test for writing it and round-tripping it, where both cases use quoted string, which is still accepted by cgit.

Issue #681

[filipnavara]

I don't think the code coverage metric is calculated correctly if it decreased with added test coverage, or am I missing something?

[mcuadros]

@filipnavara don't worry, this small changes in coverages are irrelevant.