Add match option to Nebulex.Caching

[polmiro]

Sometimes one wants to conditionally cache a value based on the result of the underlying function logic. This is easy to achieve by using the lower-level APIs Cache.get and Cache.set but it is fairly verbose and repeatable. This PR adds a new option to the Nebulex.Caching DSL to support it. For example, a classic use case would be avoiding caching the result of a REST API when a transient error is returned.

This PR adds a new option :match that takes a function with one argument. The function will be called with the value in the cache and the cache will be updated based on the boolean result returned.

[coveralls]

Coverage remained the same at 100.0% when pulling 6ac0560 on polmiro:cache-with-match into 48215f3 on cabol:master.

[cabol]

@polmiro only one silly comment, other thank that, very very nice job man, thank you very much for your contribution, this is a very cool feature 😃 👍

[polmiro]

Thinking now about naming, I am wondering if the option should be named if instead of match? What do you think?

[cabol]

Thinking now about naming, I am wondering if the option should be named if instead of match? What do you think?

I like match, I think it is clear enough and self-descriptive, we can keep it like that for now, until we come up with a better idea I guess 😄

[polmiro]

Sounds good! It's ready then :)