feat: rewrite programming-challenges CLI (#3)

challenges/hello-world/solutions/c/function/README.md

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+# hello-world/c/function
+
+Created by [@Divlo](https://github.com/Divlo) on 6 June 2021.

challenges/hello-world/solutions/c/function/solution.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+int main() {
+  char input[1024];
+  while (scanf("%s", &input) != EOF) {
+    printf("Hello, %s!", input);
+  }
+  return 0;
+}