Change knox to aws-sdk in order to support v4 aws signatures

[andreialecu]

See #29

There are some minor potential breaking changes since now aws-sdk style parameters are expected instead of knox style parameters.

So for example headers will now expect CacheControl instead of the HTTP Cache-Control knox works with.

[antony]

Any chance of this making it into the main codebase? The library is simply broken in frankfurt without it.

[jrbenito]

@hughsk,

This is really an important feature. Could you please merge this and bump version on npm?

Thanks

[andreialecu]

You can use my fork at https://github.com/andreialecu/s3-sync-aws which has this.

It's also on npm as s3-sync-aws