Add Translation Memory eXchange (TMX) support

TMX is an XML specification for the exchange of translation memory data between computer-aided translation and localization tools with little or no loss of critical data. See https://en.wikipedia.org/wiki/Translation_Memory_eXchange

extensions/xml/package.json

@@ -45,6 +45,7 @@
 				".svg",
 				".targets",
 				".tld",
+        ".tmx",
 				".vbproj",
 				".vbproj.user",
 				".vcxproj",