Add proxy support for fetch_deps.
Fix saveURLToDep to properly write files to disk.
Merge pull request #34 from ryanvanoss/proxy-support-for-fetch-deps

Add proxy support for fetch_deps.
Website and README update.

 - Add more info about using Yeti with CI to the website.
 - Focus on installation on Yeti docs on the landing page.
 - First paragraph of README introduces what it does in detail.