AWS Agent

Access AWS sigv4 resources from your browser! Allows your browser to access resources that require AWS Sigv4 signatures. Inspired by [carsales/aws-request-signer](https://github.com/carsales/aws-request-signer). Main differences from carsales/aws-request-signer: - They basically rolled their own signature process vs I rely on mhart's excellent libraries. In Firefox (and presumably elsewhere) I use [mhart/aws4fetch](https://github.com/mhart/aws4fetch) to handle all heavy lifting. This has the perk of using the browser's WebCrypto API, which should be insanely faster. In Chrome I use [mhart/aws4](https://github.com/mhart/aws4) because Chrome still has zero async support for webRequest.onBeforeSendHeaders. - This extension triggers on all AWS services instead of filtering for one. - Instance Profile credentials aren't supported as I have no use for them but could be added fairly trivially. - Chrome/Firefox/Opera support.