adding upload_s3 script

@fertel - this is a sample shell script that I've been using to upload js files to s3. There are notes in the script itself, but the basic gist:

1) The script composes the curl command you'll need to sign and upload a .js file to the cdn.adjs.net bucket.
2) Some values are hardcoded at the moment. 
3) As of now the script can be used easily to:

upload_s3.sh publisher.ad.js

...and get the latest version of publisher.ad.js up onto s3, with the correct permissions, content-type and if-modified-since headers. Slight modifications need to be made to handle HTML files, you can read more from the code comments. Also, I've redacted the S3 credentials because this repo is public.

Let me know if you need anything else to get this all Cake-ified.

Cheers,

--afsheenb