Added a CLEANUP mechanism to the exception handling library. Fixed a bug in the way setjmp() return codes were being handled that lead to infinite loops in some cases, exceptions getting missed in others. Made FINALLY {} a required element (unfortunately).

demo/skeleton.c

@@ -0,0 +1,10 @@
+#include "exclib.h"
+
+int main(void)
+{
+  TRY {
+  } CLEANUP {
+  } EXCEPT {
+  } FINALLY {
+  } ETRY;
+}