added header files for String and StringValue

String.h

@@ -0,0 +1,41 @@
+#pragma once
+#include <iostream>
+#include "StringValue.h"
+
+
+
+/* Design decisions:
+ *              - Everything related to ref-counting is the responsibility of the StringValue class
+ *              - Anything dynamically allocated is owned (and thus once deleted) by the StringValue class
+ *                (including itself -- this is possible because of the reference counting mechanism) */
+class String
+{
+private:
+
+    StringValue* _str;
+
+public:
+
+    String();
+    String(const char*);
+    String(const String&);
+    String& operator=(String);
+    String(String&&);
+    ~String();
+
+    friend void swap(String&, String&) noexcept;
+    String operator+(const String&) const;
+    String& operator+=(const String&);
+    String operator+(char) const;
+    String& operator+=(char);
+    bool operator==(const String&) const;
+    const char& operator[](size_t) const;
+    char& operator[](size_t);
+
+    size_t size() const;    // does not include null-terminator
+    const char* c_str() const;
+
+    friend std::istream& operator>>(std::istream&, String&);
+};
+
+std::ostream& operator<<(std::ostream&, const String&);