Add project files.

AS1024.GeoFeed/GeoFeedBuilder/GeoFeedTools.cs

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+using AS1024.GeoFeed.Models;
+using System.Text;
+
+namespace AS1024.GeoFeed.GeoFeedBuilder
+{
+    public static class GeoFeedTools
+    {
+        public static string ToGeoFeedCsv(this List<IPGeoFeed> geoFeeds)
+        {
+            StringBuilder csvContent = new();
+
+            foreach (var feed in geoFeeds)
+            {
+                csvContent.AppendLine($"{feed.Prefix},{feed.GeolocCountry},{feed.GeolocRegion},{feed.GeolocCity}");
+            }
+
+            return csvContent.ToString();
+        }
+    }
+}