MarkdownConverter: Add AbbreviationExtension.

Change-Id: Ib718177935b05b35c4be2d9979975c261e774743
diff --git a/src/main/java/eu/mulk/mulkcms2/common/markdown/MarkdownConverter.java b/src/main/java/eu/mulk/mulkcms2/common/markdown/MarkdownConverter.java
index 75f6c8d..4286e25 100644
--- a/src/main/java/eu/mulk/mulkcms2/common/markdown/MarkdownConverter.java
+++ b/src/main/java/eu/mulk/mulkcms2/common/markdown/MarkdownConverter.java
@@ -32,7 +32,8 @@
             AutolinkExtension.create(),
             DefinitionExtension.create(),
             TypographicExtension.create(),
-            FootnoteExtension.create()));
+            FootnoteExtension.create(),
+            AbbreviationExtension.create()));
     options.set(Parser.FENCED_CODE_BLOCK_PARSER, true);
     options.set(HtmlRenderer.SOFT_BREAK, "\n");
     options.set(HtmlRenderer.HARD_BREAK, "<br />\n");