Fix broken links

jMonkeyEngine 3 Tutorial (6) - Hello Materials
Materials forum thread - http://jmonkeyengine.org/forum/index.php?topic=14179.0
jME3 Materials documentation (PDF) - http://jmonkeyengine.googlecode.com/files/jME3_materials.pdf
Creating textures in Blender - https://www.blender.org/education-help/tutorials/materials/
Various Material screenshots - http://www.shaders.org/ifw2_textures/whatsin10.htm

src/docs/asciidoc/jme3/beginner/hello_material.adoc

@@ -384,8 +384,8 @@ See also
 
 *  <<jme3/intermediate/how_to_use_materials#,How to Use Materials>>
 *  <<sdk/material_editing#,Material Editing>>
-*  link:http://www.jmonkeyengine.com/forum/index.php?topic=14179.0[Materials] forum thread
-*  link:http://jmonkeyengine.googlecode.com/files/jME3_materials.pdf[jME3 Materials documentation] (PDF)
+*  link:https://hub.jmonkeyengine.org/t/jmonkeyengine3-material-system-full-explanation/12947[Materials] forum thread
+*  link:https://github.com/jMonkeyEngine/wiki/blob/master/src/docs/resources/tutorials/material/jME3_materials.pdf[jME3 Materials documentation (PDF)]
 *  link:http://www.youtube.com/watch?v=Feu3-mrpolc[Video Tutorial: Editing and Assigning Materials to Models in jMonkeyEngine SDK (from 2010, is there a newer one?]
-*  link:http://www.blender.org/education-help/tutorials/materials/[Creating textures in Blender]
-*  link:http://www.shaders.org/ifw2_textures/whatsin10.htm[Various Material screenshots] (Not done with JME3, this is just to show the fantastic range of Material parameters in the hands of an expert, until we have a JME3 demo for it.)
+*  link:https://www.blender.org/support/tutorials/[Creating textures in Blender]
+*  link:http://www.shaders.co.uk/ifw2_textures/whatsin10.htm[Various Material screenshots] (Not done with JME3, this is just to show the fantastic range of Material parameters in the hands of an expert, until we have a JME3 demo for it.)