Merge pull request #426 from righettod/master

Add the expression for the "doT.js" and the "dust.js" template engines

Source:

- https://github.com/epinna/tplmap/tree/master/plugins/engines
- https://olado.github.io/doT/index.html
- http://www.dustjs.com/

Fuzzing/template-engines-expression.txt

@@ -5,3 +5,5 @@
 #{42*42}
 ${42*42}
 <%=42*42 %>
+{{=42*42}}
+{^xyzm42}1764{/xyzm42}