feat(solutions): add is-palindrome/c/function

challenges/is-palindrome/solutions/c/function/solution.c

@@ -0,0 +1,18 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "character.h"
+#include "input.h"
+#include "string.h"
+
+int main() {
+  char* string = input();
+  string = string_to_upper(string);
+  string = string_replace(string, ' ', '\0');
+  bool is_palindrome = string_is_palindrome(string);
+  free(string);
+  printf("%s\n", is_palindrome ? "true" : "false");
+  return EXIT_SUCCESS;
+}