feat: Allow expressions to be terminated/sequenced by ;

Note that ultimately a terminated sequence may have
   a slightly different semantics (applying streams
   to `_|_`, most likely) but for now they don't.

trans/javascript.str

@@ -1,10 +1,6 @@
 module javascript
 imports libstrategolib signatures/- util
 
-signature
-  constructors
-    TopLevel: Ex -> Ex
-
 rules
   js: TopLevel(x) -> $[const Stdio = {
     gets: v => { process.stdout.write(String(v)); return Stdio; },
@@ -15,12 +11,13 @@ rules
   }
   [x]]
 
-  js: Stream() -> $[Stdio]
-  js: Int(x) -> x
-  js: Sum(x,y) -> $[[x] + [y]]
-  js: Gets(x, y) -> $[[x].gets([y])]
-  js: To(x, y) -> $[to([x],[y])]
-  js: Sequence(l) -> <join(|";\n")>l
+  js: Stream()     -> $[Stdio]
+  js: Int(x)       -> x
+  js: Sum(x,y)     -> $[[x] + [y]]
+  js: Gets(x, y)   -> $[[x].gets([y])]
+  js: To(x, y)     -> $[to([x],[y])]
+  js: Terminate(x) -> x
+  js: Sequence(l)  -> <join(|";\n")>l
 
 strategies