Add support for Swift 5.1

[Andrea-Scuderi]

Is your feature request related to a problem? Please describe.
Support the new release of swift 5.1

Describe the solution you'd like
The solution must be compatible with swift 5.*

[Andrea-Scuderi]

The branch feature/swift-5.1 contains the new version supporting swift 5.1.
FIX: HelloWorld and HTTPSRequest

TODO:

• S3Test broken
• Improve the swift version configuration by moving the required files in the docker/$(SWIFT_VERSION) path

[Andrea-Scuderi]

DONE:
The package now supports both swift 5.0 and swift 5.1.

TODO: S3Test broken
It's required to fix the aws-sdk to work with swift 5.1

[Andrea-Scuderi]

Fixed by release 1.0.0-alpha.2