feat(solutions): add prefix-suffix/c/function

challenges/prefix-suffix/solutions/c/function/character.h

@@ -0,0 +1,13 @@
+#ifndef __CHARACTER__
+#define __CHARACTER__
+
+/**
+ * @brief Append a character to a string, assuming string points to an array
+ * with enough space.
+ *
+ * @param string
+ * @param character
+ */
+void character_append(char* string, char character);
+
+#endif