Refined Stratified Sampling Class

[mds2120]

• [x] Make a subclass of StratifiedSampling
• [x] Add documentation for the Refinement class its subclasses.
• [x] Allow RefinedStratifiedSampling to take, as input, either a TrueStratifiedSampling object or a RefinedStratifiedSampling object
• [x] Rewrite RefinedStrafiedSampling documentation to reflect what is actually in the code.
• [x] Rename refined_stratified_sampling class to refinement and update SimpleRefinement to RandomRefinement
• [x] Add run() method to documentation and make the append_samples() method private
• [x] Rename examples to be informative and update them to reflect updated names.
• [x] Examples need to be modified for the new class structure.
• [x] Check the test failure of Voronoi GE-RSS