Add project files.

RPGLibrary.Implementation/Attribute/StrengthAttribute.cs

@@ -0,0 +1,20 @@
+using RPGLibrary.Abstraction.Attribute;
+
+namespace RPGLibrary.Implementation
+{
+  public class StrengthAttribute : IAttribute
+  {
+    public StrengthAttribute(double value)
+    {
+      Value = value;
+    }
+
+    public double Value { get; }
+
+    public override string? ToString()
+    {
+      return $"Strength: {Value}";
+    }
+  }
+
+}