GitHub Releases Helper

This PR adds an app to `tools` to be used in CI scenarios - given a repo and a token, it will roll through all of the Releases for a repo looking for NuGet packages, and build a Release directory out of them. Use this tool to build the Release directory before you call `--releasify` to create delta releases. 

```
Usage: SyncGitHubReleases.exe command [OPTS]
Builds a Releases directory from releases on GitHub

Options:
  -h, -?, --help             Display Help and exit
  -r, --releaseDir=VALUE     Path to a release directory to download to
  -u, --repoUrl=VALUE        The URL to the repository root page
  -t, --token=VALUE          The OAuth token to use as login credentials
```