Removed an un-used const.
Renamed an internal constant.

Replaced an awkward plural private constant name.
Moved service-specific resources into services/

Moved service-specific resource extensions from `lib/aws-sdk-resources/`
into `lib/aws-sdk-resources/services/`; Ditto for service-specific spec
files inside of `spec/`.

This keeps service specific code/classes separate from generic resource
implementations.
Moved a few S3 autoloads up to the S3 module.
Removed a S3 waiter fix.
Simplified regional endpoint expansion.