Allow SVGs to be proxied

Resolves #13 (closed)

I didn't add SVG as an output format due to SVGs potential to be used for malicious purposes(see https://cofense.com/blog/svg-files-abused-in-emerging-campaigns/ for more information, I'm not too familiar with the subject but ran across it) but this will still allow SVGs to get processed into a different format in the backend and sent as that, which will be safe for the end user.