Solve focus even if there is no V or U shaped data.

[simontorres]

The application should always return a focus value even if the data does not have an ideal range (that's what I mean by V or U shape)
The solution implemented in #12 works but I'm not fully convinced is the best solution.

Current Implementation

To obtain the best focus it uses the Brent optmization method with a bracket that has to define a V or U shape data.

Idea for Implementation

It should implement diferentiated algorithm to get the best focus, depending on the shape of the data.