Better makefile, restructured, more demos

demo/threelevel.c

@@ -0,0 +1,16 @@
+#include "exclib.h"
+
+int main(void)
+{
+  TRY {
+    TRY {
+      THROW(3, NULL);
+    } CATCH(5) {
+      EXCLIB_TRACE("Caught 5");
+    } ETRY;
+  } CATCH(3) {
+    EXCLIB_TRACE("Caught 3");
+  } ETRY;
+
+  return 0;
+}