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

challenges/is-palindrome/solutions/c/function/character.h

@@ -0,0 +1,21 @@
+#ifndef CHARACTER_H
+#define CHARACTER_H
+
+/**
+ * @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);
+
+/**
+ * @brief Converts the character to uppercase.
+ *
+ * @param character
+ * @return const char
+ */
+const char character_to_upper(const char character);
+
+#endif