(GH-25) Add default values for issue priority

src/Cake.Issues/IssuePriority.cs

@@ -0,0 +1,33 @@
+namespace Cake.Issues
+{
+    /// <summary>
+    /// Default priorities for <see cref="IIssue.Priority"/>.
+    /// </summary>
+    public enum IssuePriority
+    {
+        /// <summary>
+        /// Undefined priority.
+        /// </summary>
+        Undefined = 0,
+
+        /// <summary>
+        /// Issues which brings attention to a specific part of the code or recommends a way of improvement.
+        /// </summary>
+        Hint = 100,
+
+        /// <summary>
+        /// Issues which aren't necessarily bad or wrong, but probably useful to know.
+        /// </summary>
+        Suggestion = 200,
+
+        /// <summary>
+        /// Issues that do not prevent code from compiling but may nevertheless represent serious coding inefficiencies.
+        /// </summary>
+        Warning = 300,
+
+        /// <summary>
+        /// Issues that either prevent code from compiling or result in runtime errors.
+        /// </summary>
+        Error = 400
+    }
+}