Travis: Test KS and Github releases with netkan.exe

Yes, it's that code you've always been wanting.

Now when pull requests are made to NetKAN, we'll grab the latest `netkan.exe` and run it over the files changed in the PR. This means we're not trying to download 200+ different mods, instead it's just the couple that the user wants changed.

The output isn't particuarly pretty when it fails, but [this travis output](https://travis-ci.org/pjf/NetKAN/builds/43913077) has an example, starting at line 1299. The output will be prettier if `netkan.exe` produces prettier output on failure, and we already want to improve that. :) Note that output also includes a passing file, to show that it picks up a passed netkan run correctly (passes are only reported in the summary, in this case line 1322 - failed 2/3 subtests).

When we're not part of a pull request, this code is skipped.

@Sircmpwn has given permission over IRC to download files from KS as part of CI testing, and since I imagine travis has very close data ties to github, and we're *only* downloading mods when their netkan files have changed, I doubt we'll be considered impolite there.

~ Paul