Add support for gif & jpeg images (#370)

* Add support for gif images

* include jpeg support as well

Author: Mpdreamz

docs/syntax/images.md

@@ -44,6 +44,21 @@ Here is the same image used inline ![Elasticsearch](img/observability.png)
 
 Here is the same image used inline ![Elasticsearch](img/observability.png)
 
+### SVG 
+
+```markdown
+![Elasticsearch](img/alerts.svg)
+```
+![Elasticsearch](img/alerts.svg)
+
+### GIF
+
+```markdown
+![Elasticsearch](img/timeslider.gif)
+```
+![Elasticsearch](img/timeslider.gif)
+
+
 ## Asciidoc syntax
 
 ```asciidoc

docs/syntax/img/alerts.svg

@@ -48,6 +48,9 @@ public DocumentationSet(BuildContext context)
 			.Select(f => context.ReadFileSystem.FileInfo.New(f))
 			.Select<IFileInfo, DocumentationFile>(file => file.Extension switch
 			{
+				".jpg" => new ImageFile(file, SourcePath, "image/jpeg"),
+				".jpeg" => new ImageFile(file, SourcePath, "image/jpeg"),
+				".gif" => new ImageFile(file, SourcePath, "image/gif"),
 				".svg" => new ImageFile(file, SourcePath, "image/svg+xml"),
 				".png" => new ImageFile(file, SourcePath),
 				".md" => CreateMarkDownFile(file, context),