Updated AWS Config code examples (#597)

* Renamed config-helloword as show-resource-history; added delete-configuration-recorder, delete-delivery-channel, enable-config, list-configuration-recorders, list-delivery-channels, and list-resources code examples; all for AWS Config

* Updated AWS Config sync code example to use latest code style

* Updated AWS Config code examples based on feedback; uses latest code style

* Added config-helloworld.rs back to config code examples

* Updated Config code examples to use asynchronous Config

* Updated Config code examples to alpha 0.0.17 bits

* Updated Config hello world code example

* Added readme file for AWS Config code examples; updated internal docs in config-helloworld code example

* Added info about AWS Config code examples to SDK change log.

* Updated AWS Config code examples based on feedback.

* Fixed typos in AWS Config code examples

* Updated AWS Config code examples to include unit tests, readme, moved operations from main into separate function.

* Removed unit tests from AWS Config code examples.

* Remove `actix-rt` dependency