Various cleanups.

* Remove disused macro.
* GCC doesn't seem to mind if IGNORE() is left off.
* Enumify phase codes.
* Use EXIT_* macros in all exit() calls.
* How did this even work without extern?
* Give advent.h a much-needed makeover.
* Use the chomp indicator in YAML string blocks to avoid code ugliness.

main.c

@@ -13,7 +13,7 @@
  * and for the offensive globals.  Applying the Structured Program
  * Theorem can be hard.
  */
-#define DEFINE_GLOBALS_FROM_INCLUDES
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdbool.h>
@@ -42,7 +42,7 @@ static void sig_handler(int signo)
         if (logfp != NULL)
             fflush(logfp);
     }
-    exit(0);
+    exit(EXIT_FAILURE);
 }
 // LCOV_EXCL_STOP
 
@@ -113,7 +113,7 @@ int main(int argc, char *argv[])
 #endif
             fprintf(stderr,
                     "        -s suppress command editing\n");
-            exit(-1);
+            exit(EXIT_FAILURE);
             break;
         }
     }