Next enhancements

[galvesribeiro]

• Make interfaces for both storages so it can make components testable
• Make the concrete storage classes to have internal ctors

[celluj34]

First one can be checked off now, right?

The second one can too, now that the implementations are marked internal.

[smartprogrammer93]

Please update the README.md file to reflect these changes

[celluj34]

Done! Have a look at #49