Doc: Generate 4D example illustration data

The illustration data were generated with 128 projections on a 512 x 512 x 128
projection stack with 1 mm detector spacing.

The illustration reconstructions were generated on a 256 x 128 x 256 x 8 grid
with 0.5 mm spatial spacing.

Author: axel-grc

documentation/docs/ExternalData/FourDConjugateGradient.gif.sha512

@@ -0,0 +1 @@
+430dd919f1ad889d78a04cc70c32f1851b790f0423d6ee63ae3a9c626786a3fe9617a38b5655cecfb1890f56e6ffe298a01fe2d39210a7f7a16e539074b3f259

documentation/docs/ExternalData/FourDFDK.gif.sha512

@@ -0,0 +1 @@
+6db1332af81b0ac92d9fbbf3ad42ce8d3f7c839923e979cd4aa7bb1285e7b1f482221d77c7983547020317ab652b1b05d998916f0952f96c741b58d37a0b2c80

documentation/docs/ExternalData/FourDRooster.gif.sha512

@@ -0,0 +1 @@
+6db1332af81b0ac92d9fbbf3ad42ce8d3f7c839923e979cd4aa7bb1285e7b1f482221d77c7983547020317ab652b1b05d998916f0952f96c741b58d37a0b2c80

examples/FourDConjugateGradient/README.md

@@ -3,6 +3,8 @@
 This example shows how to perform iterative cone-beam CT reconstruction using either CPU or GPU resources.
 It reads its data from disk. The data can be generated by the [*Generate 4D data* example](../GenerateFourDData/README.md) or [downloaded from Girder](https://data.kitware.com/#collection/5a7706878d777f0649e04776/folder/69611c373b9bcc32c3188531).
 
+![img_4D](../../documentation/docs/ExternalData/FourDConjugateGradient.gif){w=200px alt="conjugate gradient 4D reconstruction"}
+
 `````{tab-set}
 
 ````{tab-item} C++
@@ -11,5 +13,11 @@ It reads its data from disk. The data can be generated by the [*Generate 4D data
 :language: c++
 ```
 ````
+````{tab-item} Python
+
+```{literalinclude} ./FourDConjugateGradient.py
+:language: python
+```
+````
 
 `````

examples/FourDFDK/README.md

@@ -3,6 +3,8 @@
 This example shows how to perform filtered backprojection cone-beam CT reconstruction using either CPU or GPU resources depending on how RTK was compiled.
 It reads its data from disk. The data can be generated by the [*Generate 4D data* example](../GenerateFourDData/README.md) or [downloaded from Girder](https://data.kitware.com/#collection/5a7706878d777f0649e04776/folder/69611c373b9bcc32c3188531).
 
+![img_4D](../../documentation/docs/ExternalData/FourDFDK.gif){w=200px alt="Fdk 4D reconstruction"}
+
 `````{tab-set}
 
 ````{tab-item} C++
@@ -12,4 +14,11 @@ It reads its data from disk. The data can be generated by the [*Generate 4D data
 ```
 ````
 
+````{tab-item} Python
+
+```{literalinclude} ./FourDFDK.py
+:language: python
+```
+````
+
 `````

examples/FourDROOSTER/README.md

@@ -3,6 +3,8 @@
 This example shows how to perform iterative cone-beam CT reconstruction using either CPU or GPU resources.
 It reads its data from disk. The data can be generated by the [*Generate 4D data* example](../GenerateFourDData/README.md) or [downloaded from Girder](https://data.kitware.com/#collection/5a7706878d777f0649e04776/folder/69611c373b9bcc32c3188531).
 
+![img_3D](../../documentation/docs/ExternalData/FourDRooster.gif){w=200px alt="Rooster 4D reconstruction"}
+
 `````{tab-set}
 
 ````{tab-item} C++