changed the assimp output directory vars to cached vars

CMakeLists.txt

@@ -334,9 +334,9 @@ INCLUDE (FindPkgMacros)
 INCLUDE (PrecompiledHeader)
 
 # Set Assimp project output directory variables.
-SET(ASSIMP_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/bin")
-SET(ASSIMP_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/bin")
-SET(ASSIMP_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/lib")
+SET(ASSIMP_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/bin" CACHE STRING "Path for runtime output files")
+SET(ASSIMP_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/bin" CACHE STRING "Path for library output files")
+SET(ASSIMP_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/lib" CACHE STRING "Path for archive output files")
 
 # Macro used to set the output directories of a target to the
 # respective Assimp output directories.