Add Experimental Windows Support

[brianmichel]

This should build (but not completely test) on Windows. I would label it as experimental since it does run, but will likely have issues that need to be ironed out. As mentioned in https://github.com/segmentio/analytics-swift/issues/279 a pluggable networking stack will help us work around the problems with URLSession but I figured I'd post this as a mergable artifact.

Changes

• This adds an .editorconfig so that style can be kept consistent across those who are using Xcode and other editors (I don't know if theseis the right settings, but I tried to match what was there)
• Add a new WindowsVendorSystem with system calls to populate various bits of information where possible.
• Update #if blocks around the codebase to allow for building on Windows
• Add entry for Windows CI to ensure that the codebase stays buildable on Windows.

I apologize for the trimming of the whitespace, I can try to rebuild this PR if it's an annoyance, but it seems that VS Code trims whitespace by default and this is where I ended up.

[brianmichel]

~~Rebasing is blocked until https://github.com/segmentio/JSONSafeEncoder-Swift/pull/1 (or some variant of this) lands~~

[brianmichel]

@bsneed this should be ready for review if you'd like

[bsneed]

cc @alanjcharles

[bsneed]

Closing this in lieu of the merged/updated PR #348