Added filesystem stuff on Linux

More includes for Linux
Update build script to copy assets and compile shaders
Added base code directory as include path
Added FS_SystemPath
Made asset loading work directory agnostic

code/core/platform.h

@@ -70,9 +70,14 @@
 	#include <windows.h>
 	#pragma warning(disable : 4201)
 #elif OS_LINUX
+	#include <sys/types.h>
 	#include <dlfcn.h>
 	#include <sys/mman.h>
 	#include <unistd.h>
+	#include <fcntl.h>
+	#include <sys/stat.h>
+	#include <errno.h>
+	#include <dirent.h>
 #endif
 
 #endif  // LD_CORE_PLATFORM_H_