Provide a mechanism to use Repository<Void, C>

[SpicyCactuar]

Summary

Sometimes a user may want to make a change to data locally or in API, but the 'response' contains no data.

The issue is the following:

• User instantiates a Repository<Void, C>.
• It has to provide a QueryStrategy<Void, C>.
• QueryStrategy#read would return Void.
• It can't return null since Repository would interpret it as a cache miss. Void cannot be instantiated.
• The user is forced to return something, Object for example. In consequence, it's forced to change the Call type parameter from Void to Object yielding a Call<Void>.

[SpicyCactuar]

One solution i came up with was having a Transaction<T>, Operation<T> or something similar that holds, at least, the following data:

• Whether the operation was a hit or a miss. Let's call it status for now.
• The data yielded by said operation, if any. Let's call it data for now.

This way, we check the status instead of the data.

What do you think @juanignaciomolina ?