Move CSFML source files to CSFML/ directory

This helps make it easier to distinguish SFML files from CSFML files.
This is especially important for CSFML private headers which are
often C++ code with .hpp file extensions. This change means SFML and
CSFML can use headers with the same name without conflict.

CMakeLists.txt

@@ -61,7 +61,7 @@ if(SFML_OS_WINDOWS)
 endif()
 
 # add the subdirectories
-add_subdirectory(src/SFML)
+add_subdirectory(src/CSFML)
 if(CSFML_BUILD_DOC)
     add_subdirectory(doc)
 endif()