Added PDUOption::to<>. TCP options now use this method when being converted to their appropriate types.

include/internals.h

@@ -99,14 +99,14 @@ private:
 void skip_line(std::istream &input);
 bool from_hex(const std::string &str, uint32_t &result);
 
-template<bool, typename>
+template<bool, typename T = void>
 struct enable_if {
-    
+    typedef T type;
 };
 
 template<typename T>
-struct enable_if<true, T> {
-    typedef T type;
+struct enable_if<false, T> {
+    
 };
 
 PDU *pdu_from_flag(Constants::Ethernet::e flag, const uint8_t *buffer, 
@@ -173,6 +173,31 @@ HWAddress<n> last_address_from_mask(HWAddress<n> addr, const HWAddress<n> &mask)
 inline bool is_dot3(const uint8_t *ptr, size_t sz) {
     return (sz >= 13 && ptr[12] < 8);
 }
+
+template<typename T>
+struct is_unsigned_integral {
+    static const bool value = false;
+};
+
+template<>
+struct is_unsigned_integral<uint8_t> {
+    static const bool value = true;
+};
+
+template<>
+struct is_unsigned_integral<uint16_t> {
+    static const bool value = true;
+};
+
+template<>
+struct is_unsigned_integral<uint32_t> {
+    static const bool value = true;
+};
+
+template<>
+struct is_unsigned_integral<uint64_t> {
+    static const bool value = true;
+};
 } // namespace Internals
 } // namespace Tins
 /**