adding example 2

Added Mikkel's example and updated the documentation

Will resolve issue #52 (closed)

@mikf and @mmpe -- one interesting thing: the example does not push the turbines all the way to the edge of the boundary. Not sure if it should, though? Also, NOJ model has lower AEP than GCL. Just fun facts.

docs/source/examples/example_2_wake_comparison.rst

+.. Example 2
+
+Example 2: Optimization with Different Wake Models
+===================================================
+
+This example demonstrates the optimization of a 3-turbine farm with
+the N. O. Jensen (NOJ) and G. C. Larsen (GCL) wake models implemented in
+FUSED-Wake.
+
+Specifications
+--------------
+
+- The farm is offshore.  
+- The wind resource is defined by arrays of the frequency and Weibull
+  A and k parameters taken from a Horns Rev calculation.  
+- There is a boundary beyond which the turbines cannot go.  
+- The turbines cannot be closer than 2D.
+
+Results
+-------
+
+The optimization results are visualized in the figure below, and the
+script also outputs the following information on the resultings costs::
+
+   Comparison of cost models vs. optimized locations:
+   
+   Cost    |    GCL_aep      NOJ_aep
+   ---------------------------------
+   GCL_loc |   -2704.40    -2688.57   (0.59%)
+   NOJ_loc |   -2703.90    -2688.59   (0.57%)
+                (0.02%)     (-0.00%)
+
+The subscript ``_aep`` indicates the AEP calculated using the specified wake
+model. The subscript ``_loc`` indicates the optimal locations determined when
+optimizing with the specified wake model. For example, the cost corresponding
+to the ``GCL_aep`` column and the ``NOJ_loc`` column is the AEP calculated
+using the GCL wake model for the optimal location results when the N. O.
+Jensen wake model was used in the optimization. The percentages in parentheses
+are the percent differences for the column or row.  
+
+Important observations:  
+
+- The upper and lower turbines are pushed away from each other, towards
+  the corners.  
+- There is little difference in the AEP value when calculated using either of
+  the optimal locations, since the optimal locations themselves are quite
+  close.  
+- The N. O. Jensen wake model has an AEP that is approximately 0.6% lower than
+  the AEP with the G. C. Larsen wake model for this farm.  
+
+.. figure:: /../../examples/example_2_wake_comparison.png
+
+Code
+----
+
+.. literalinclude:: /../../examples/example_2_wake_comparison.py