[#40] Provide cleaner contracts

[maypok86]

Problem

Now otter uses an api very similar to other go cache libraries, but unfortunately it is not particularly beautiful and extensible.

For example, now we have Set(key, value) and SetWithTTL(key, value, ttl) functions, but if we want to add SetIfAbsent(key, value) function, we also need SetIfAbsentWithTTL(key, value, ttl) function, which doesn't look nice anymore.

Solution

Implement a more advanced version of the builder and a set of cache wrappers.

Related issue(s)

• Resolves Cleaner api contracts #40

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