Add public interface with factory methods, hide implementation

[HomeOfTheWizard]

• Create a public interface with static factory methods
• make implementation class private
• replace usage of impl class constructor with interface factory methods

[henryx]

Thank you for the PR. Because I cannot founded a simple method to solve conflicts, I've merged this PR manually (see referenced commits)

[HomeOfTheWizard]

Thank you. My bad, I think I forgot to tick the box to allow you editing the PR so you could resolve the conflicts. For future PRs, I would like to help you maintain the library if you are willing to give write access to the repo.