Implemented operator< on both HWAddress and IPv4Address.

include/hw_address.h

@@ -206,6 +206,17 @@ public:
         return !(*this == rhs);
     }
     
+    /**
+     * \brief Compares this HWAddress for less-than inequality.
+     * 
+     * \param rhs The HWAddress to be compared to.
+     * 
+     * \return bool indicating whether this address is less-than rhs.
+     */
+    bool operator<(const HWAddress &rhs) const {
+        return std::lexicographical_compare(begin(), end(), rhs.begin(), rhs.end());
+    }
+    
     /**
      * \brief Retrieves the size of this address.
      * 

include/ip_address.h

@@ -110,6 +110,16 @@ namespace Tins {
             return !(*this == rhs);
         }
         
+        /**
+         * \brief Compare this IPv4Address for less-than inequality.
+         * 
+         * \param rhs The address to be compared.
+         * \return bool indicating whether this address is less-than rhs.
+         */
+        bool operator< (const IPv4Address &rhs) const {
+            return ip_addr < rhs.ip_addr;
+        }
+        
         /**
          * \brief Writes this address to a std::ostream.
          *