Update URLs to ITK documentation.

Author: zivy

Python/60_Registration_Introduction.ipynb

@@ -60,28 +60,28 @@
     "### Optimizers\n",
     "\n",
     "Several optimizer types are supported via the `SetOptimizerAsX()` methods. These include:\n",
-    "* [Exhaustive](http://www.itk.org/Doxygen/html/classitk_1_1ExhaustiveOptimizerv4.html)\n",
-    "* [Nelder-Mead downhill simplex](http://www.itk.org/Doxygen/html/classitk_1_1AmoebaOptimizerv4.html), a.k.a. Amoeba\n",
-    "* [Powell optimizer](https://itk.org/Doxygen/html/classitk_1_1PowellOptimizerv4.html)\n",
-    "* [1+1 evolutionary optimizer](https://itk.org/Doxygen/html/classitk_1_1OnePlusOneEvolutionaryOptimizerv4.html)\n",
+    "* [Exhaustive](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1ExhaustiveOptimizerv4.html)\n",
+    "* [Nelder-Mead downhill simplex](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1AmoebaOptimizerv4.html), a.k.a. Amoeba\n",
+    "* [Powell optimizer](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1PowellOptimizerv4.html)\n",
+    "* [1+1 evolutionary optimizer](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1OnePlusOneEvolutionaryOptimizerv4.html)\n",
     "* Variations on gradient descent:\n",
-    "  * [GradientDescent](http://www.itk.org/Doxygen/html/classitk_1_1GradientDescentOptimizerv4Template.html)\n",
-    "  * [GradientDescentLineSearch](http://www.itk.org/Doxygen/html/classitk_1_1GradientDescentLineSearchOptimizerv4Template.html)\n",
-    "  * [RegularStepGradientDescent](http://www.itk.org/Doxygen/html/classitk_1_1RegularStepGradientDescentOptimizerv4.html)\n",
-    "* [ConjugateGradientLineSearch](http://www.itk.org/Doxygen/html/classitk_1_1ConjugateGradientLineSearchOptimizerv4Template.html)\n",
-    "* [L-BFGS2](https://itk.org/Doxygen/html/classitk_1_1LBFGS2Optimizerv4.html) (Limited memory Broyden, Fletcher, Goldfarb, Shannon)\n",
-    "* [L-BFGS-B](http://www.itk.org/Doxygen/html/classitk_1_1LBFGSBOptimizerv4.html) (Limited memory Broyden, Fletcher, Goldfarb, Shannon - Bound Constrained) - supports the use of simple constraints.\n",
+    "  * [GradientDescent](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1GradientDescentOptimizerv4Template.html)\n",
+    "  * [GradientDescentLineSearch](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1GradientDescentLineSearchOptimizerv4Template.html)\n",
+    "  * [RegularStepGradientDescent](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1RegularStepGradientDescentOptimizerv4.html)\n",
+    "* [ConjugateGradientLineSearch](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1ConjugateGradientLineSearchOptimizerv4Template.html)\n",
+    "* [L-BFGS2](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1LBFGS2Optimizerv4Template.html) (Limited memory Broyden, Fletcher, Goldfarb, Shannon)\n",
+    "* [L-BFGS-B](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1LBFGSBOptimizerv4.html) (Limited memory Broyden, Fletcher, Goldfarb, Shannon - Bound Constrained) - supports the use of simple constraints.\n",
     "\n",
     "\n",
     "### Similarity metrics\n",
     "\n",
     "Several metric types are supported via the `SetMetricAsX()` methods. These include:\n",
-    "* [MeanSquares](http://www.itk.org/Doxygen/html/classitk_1_1MeanSquaresImageToImageMetricv4.html)\n",
-    "* [Demons](http://www.itk.org/Doxygen/html/classitk_1_1DemonsImageToImageMetricv4.html)\n",
-    "* [Correlation](http://www.itk.org/Doxygen/html/classitk_1_1CorrelationImageToImageMetricv4.html)\n",
-    "* [ANTSNeighborhoodCorrelation](http://www.itk.org/Doxygen/html/classitk_1_1ANTSNeighborhoodCorrelationImageToImageMetricv4.html)\n",
-    "* [JointHistogramMutualInformation](http://www.itk.org/Doxygen/html/classitk_1_1JointHistogramMutualInformationImageToImageMetricv4.html)\n",
-    "* [MattesMutualInformation](http://www.itk.org/Doxygen/html/classitk_1_1MattesMutualInformationImageToImageMetricv4.html)\n",
+    "* [MeanSquares](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1MeanSquaresImageToImageMetricv4.html)\n",
+    "* [Demons](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1DemonsImageToImageMetricv4.html)\n",
+    "* [Correlation](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1CorrelationImageToImageMetricv4.html)\n",
+    "* [ANTSNeighborhoodCorrelation](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1ANTSNeighborhoodCorrelationImageToImageMetricv4.html)\n",
+    "* [JointHistogramMutualInformation](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1JointHistogramMutualInformationImageToImageMetricv4.html)\n",
+    "* [MattesMutualInformation](https://docs.itk.org/projects/doxygen/en/stable/classitk_1_1MattesMutualInformationImageToImageMetricv4.html)\n",
     "\n",
     "\n",
     "### Interpolators\n",