Added strongly types conveniences methods to AttributeDictionary

To aid in retrieving strongly types values from the `AttributeDictionary`, I've added convenience methods for e.g. `GetBooleanValue()`, `GetInteger()`, &c., each corresponding to the convertible types on the `AttributeValueConverter`. This will make it easier to implement logic in view models. In addition, since `AttributeValueConverter` is currently `internal`, this allows external libraries—including `OnTopic.ViewModels`—to benefit from the the conversion logic without having to have direct access to the library.

This aids in the implementation of Feature #99.

OnTopic/Attributes/AttributeDictionary.cs

@@ -43,6 +43,60 @@ public AttributeDictionary(): base(StringComparer.OrdinalIgnoreCase) { }
       return String.IsNullOrWhiteSpace(value)? null : value;
     }
 
+    /*==========================================================================================================================
+    | METHOD: GET BOOLEAN VALUE
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Gets an attribute value as a Boolean from the <see cref="AttributeDictionary"/> based on the <paramref name="
+    ///   attributeKey"/>.
+    /// </summary>
+    /// <param name="attributeKey">The string identifier for the <see cref="AttributeRecord"/>.</param>
+    /// <returns>The value for the attribute as a boolean.</returns>
+    public bool? GetBoolean(string attributeKey) => AttributeValueConverter.Convert<bool?>(GetValue(attributeKey));
+
+    /*==========================================================================================================================
+    | METHOD: GET INTEGER
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Gets an attribute value as an integer from the <see cref="AttributeDictionary"/> based on the <paramref name="
+    ///   attributeKey"/>.
+    /// </summary>
+    /// <param name="attributeKey">The string identifier for the <see cref="AttributeRecord"/>.</param>
+    /// <returns>The value for the attribute as an integer.</returns>
+    public int? GetInteger(string attributeKey) => AttributeValueConverter.Convert<int?>(GetValue(attributeKey));
+
+    /*==========================================================================================================================
+    | METHOD: GET DOUBLE
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Gets an attribute value as a double from the <see cref="AttributeDictionary"/> based on the <paramref name="
+    ///   attributeKey"/>.
+    /// </summary>
+    /// <param name="attributeKey">The string identifier for the <see cref="AttributeRecord"/>.</param>
+    /// <returns>The value for the attribute as a double.</returns>
+    public double? GetDouble(string attributeKey) => AttributeValueConverter.Convert<double?>(GetValue(attributeKey));
+
+    /*==========================================================================================================================
+    | METHOD: GET DATETIME
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Gets an attribute value as a date/time from the <see cref="AttributeDictionary"/> based on the <paramref name="
+    ///   attributeKey"/>.
+    /// </summary>
+    /// <param name="attributeKey">The string identifier for the <see cref="AttributeRecord"/>.</param>
+    /// <returns>The value for the attribute as a DateTime object.</returns>
+    public DateTime? GetDateTime(string attributeKey) => AttributeValueConverter.Convert<DateTime?>(GetValue(attributeKey));
+
+    /*==========================================================================================================================
+    | METHOD: GET URI
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Gets an attribute value as a URI from the <see cref="AttributeDictionary"/> based on the <paramref name="attributeKey
+    ///   "/>.
+    /// </summary>
+    /// <param name="attributeKey">The string identifier for the <see cref="AttributeRecord"/>.</param>
+    /// <returns>The value for the attribute as a Uri object.</returns>
+    public Uri? GetUri(string attributeKey) => AttributeValueConverter.Convert<Uri?>(GetValue(attributeKey));
 
   } //Class
 } //Namespace