Change public interface

[xuset]

In previous discussions we have concluded that a simpler public interface would be beneficial and include the following methods:

• constructor
• update
• fetch
• getFile

The remaining public methods should be removed from the public interface.

At this point update() should also be modified to remove the old snapshots once the new snapshot is loaded in.

Related to #45

[georgeaf99]

Awesome! 👍🏻

[georgeaf99]

I am not going to do a lot of refactoring here. We can make an issue later to remove all the code that manages multiple snapshots.