added an interview section called intro which assumes programming knowlege but not java specific

added an interview section called intro which assumes programming knowlege but not java specific.
there is a bug in DoubleAverager they should find and fix. This is a quick test on whether or not they know how to code. A C#, Ruby, C++, etc developer should still be able to complete this step without knowing much java.

Then they should implement RunningAverageCalulator which averages only the last N numbers. This is mean to create the potential for futher dicussion over reuse (DoubleAverager), dependency inversion principal (how do you get your Averager<Double>), TDD, data structures (linked lists, circular queues), etc as we see fit.