Refactorize Evaluator.java

To implement a specific evaluator,
you can create a file EvaluatorSomething.java
simlar to EvaluatorAvgPrecision.java.
And then implement function
    public double evaluate( String query,
        HashMap < Integer , Double > query_revelance,
        ArrayList<ScoredDocument > query_rank)

Parsing the revalence level and assigned "rel" in Evaluator.java as
Perfect: 10.0
Excellent: 7.0
Good: 5.0
Fair: 1.0
Bad: 0.0