[webdoc121] Webdoc: particle reference; move examples from ref to ex ()

Examples/scatter2d/ParticleAcrossInterface.py

Examples/specular/AlternatingLayers1.py

Examples/specular/AlternatingLayers2.py

Sample/Particle/Compound.h

Sample/Particle/CoreAndShell.h

Sample/Particle/IParticle.h

Sample/Particle/Mesocrystal.h

Sample/Particle/Particle.h

Tests/Examples/CMakeLists.txt

...ata/ExamplesMini/scatter2d/ParticleAcrossInterface.int.gz

.../ExamplesMini/scatter2d/ParticlesCrossingInterface.int.gz

auto/Wrap/libBornAgainSample.py

auto/Wrap/libBornAgainSample_wrap.cpp

hugo/content/ex/instr/_index.md

hugo/content/ex/sample/_index.md

hugo/content/ex/sim/_index.md

...ontent/ex/sim/gisas-no-dwba-terms/CylindersInBA_setup.jpg

hugo/content/ex/sim/gisas-no-dwba-terms/index.md

hugo/content/ex/sim/gisas/CylindersInDWBA_setup.jpg

hugo/content/ex/sim/gisas/_index.md