Added EC2 code examples (#518)

* Added EC2 code examples

* Updated EC2 describe-instances example based on feedback

* Updated EC2 Cargo.toml and monitor-instances code example based on feedback

* Removed extra blank line in EC2 monitor-instances code example.

* Refactored EC2 describe-instances example to use set_instance_ids with Option(al) instance ID

* Updated EC2 code examples to use -r REGION; added new list-all-instance-events code example

* Updated EC2 list-all-instance-events code example based on feedback

* Updated S3 Cargo.toml file for code examples

* Fixed package use statements in EC2 code examples

* Tweaked EC2 hello world code example to trigger actions

* Updated EC2 code examples to use asynchronous Config

* Updated EC2 code examples after cargo fmt

* Removed references to ProvideRegion from EC2 code examples

* Updated EC2 code examples to alpha 0.0.17 bits

* Added readme file for EC2 code examples

* Updated EC2 code examples to include unit tests, readme; refactored operations from main into separate functions.

* Removed unit tests from EC2 code examples.