public SpelTaskEvaluator build () {
      return new SpelTaskEvaluator(this);
    }
a {@link TaskEvaluator} implemenation which is based on 
Spring Expression Language for resolving expressions.

@author Arik Cohen
@since Mar 31, 2017
src/main/java/com/creactiviti/piper/core/task/SpelTaskEvaluator.java