Creating simple Akka Streams

A stream is a set of components with different responsibilities. Some components consume data, some transform data, and others deliver data. Akka Streams uses these components as modular pieces that you put together to create a runnable stream. These pieces help you not only understand the overall design of your topology, but they also aid in maintainability. In addition, they are reusable, which allows us to use the don't repeat yourself (DRY) principle.

Each stream topology basically consists of the following:

• Source: This is the entry point to your stream. There must be at least one in every stream. 
• Sink: This is the exit point of your stream. There must be at least one in every stream.
• Flow: This is the component responsible for manipulating the elements of the stream. You can have none or any number of them.

These components are also known as stages. There are multiple built-in stages that allow you to do the most common operations. These operations range from...