relicense everything under CC0-1.0 or Unlicense, add SPDX ID

c-programming/experiments/bool-operations.c

@@ -2,7 +2,8 @@
  * bool-operations.c
  *
  * Author: Intel A80486DX2-66
- * License: Unlicense
+ * License: Creative Commons Zero 1.0 Universal or Unlicense
+ * SPDX-License-Identifier: CC0-1.0 OR Unlicense
  */
 
 #include <inttypes.h>

c-programming/experiments/clock-malfunction-imitation.c

@@ -9,7 +9,8 @@
  * - exponential growth of time
  *
  * Author: Intel A80486DX2-66
- * License: Unlicense
+ * License: Creative Commons Zero 1.0 Universal or Unlicense
+ * SPDX-License-Identifier: CC0-1.0 OR Unlicense
  */
 
 #include <limits.h>

c-programming/experiments/floatscan-experiment.c

@@ -32,7 +32,8 @@
  *
  * The license information of the added code and this modification:
  *     Author: Intel A80486DX2-66
- *     License: Unlicense
+ *     License: Creative Commons Zero 1.0 Universal or Unlicense
+ *     SPDX-License-Identifier: CC0-1.0 OR Unlicense
  */
 
 #include <ctype.h>

c-programming/experiments/reverse-ramdisk.c

@@ -23,7 +23,8 @@
  * TODO: Test: Automate the test verification
  *
  * Author: Intel A80486DX2-66
- * License: Unlicense
+ * License: Creative Commons Zero 1.0 Universal or Unlicense
+ * SPDX-License-Identifier: CC0-1.0 OR Unlicense
  */
 
 #include <errno.h>

c-programming/experiments/static-vs-dynamic-mem-alloc.c

@@ -2,7 +2,8 @@
  * static-vs-dynamic-mem-alloc.c
  *
  * Author: Intel A80486DX2-66
- * License: Unlicense
+ * License: Creative Commons Zero 1.0 Universal or Unlicense
+ * SPDX-License-Identifier: CC0-1.0 OR Unlicense
  */
 
 #include <stdint.h>