- Remove documentation.h include and replace with forward declaration

- Move Documentation struct into documentation namespace

src/engine/configurationmanager.cpp

@@ -25,6 +25,7 @@
 #include <openspace/engine/configurationmanager.h>
 
 #include <openspace/documentation/documentation.h>
+
 #include <ghoul/filesystem/filesystem.h>
 #include <ghoul/logging/logmanager.h>
 #include <ghoul/lua/lua_helper.h>