move exercises and lectures into subfolders

Exercises/C20/ConditionalDirective/conditional_directive_example.c

@@ -0,0 +1,15 @@
+#include <stdio.h>  
+#include <conio.h>  
+
+#define DEBUG_ON 0
+
+int main(void) 
+{  
+#if DEBUG_ON == 1
+	printf("Debug mode - about to do something\n");  
+#else  
+	printf("Running in standard mode");  
+#endif  
+	
+	return 0;
+}