Properly escape element descriptions

Make sure dot is happy with the provided labels by correctly escaping
special characters inside the element descriptions.

techtree-manager/src/tree.rs

@@ -38,6 +38,13 @@ impl Element {
 
         let mut attributes = Vec::new();
 
+        let description = description
+            .replace("<", "&lt;")
+            .replace(">", "&gt;")
+            .replace("&", "&amp;")
+            .replace("'", "&apos;")
+            .replace("\"", "&quot;");
+
         attributes.push(format!(
             r##"label = <{{{{#{issue_number} | {status}}}|<I>{ty}</I>|<B>{description}</B>}}>"##
         ));