dead code elimination for JS backend; JS improvements (but doesn't work yet)

todo.txt

@@ -7,6 +7,7 @@ Debug GC session:
 New pragmas:
 - ``hoist`` pragma for loop hoisting
 - test & document ``byCopy`` pragma
+- document destructors
 
 - ``borrow`` needs to take type classes into account
 - make templates hygienic by default: try to gensym() everything in the 'block'
@@ -50,8 +51,7 @@ version 0.9.XX
 - implicit ref/ptr->var conversion; the compiler may store an object
   implicitly on the heap for write barrier efficiency; better: 
   proc specialization in the code gen
-- EcmaScript needs a new and better code gen: simply adapt the C code gen to it
-- dead code elim for JS backend; 'of' operator for JS backend
+- 'of' operator for JS backend
 - tlastmod returns wrong results on BSD (Linux, MacOS X: works)
 - nested tuple unpacking; tuple unpacking in non-var-context
 - 'nimrod def': does not always work?
@@ -104,7 +104,7 @@ Low priority
 - change how comments are part of the AST
 - ``with proc `+`(x, y: T): T`` for generic code
 - new feature: ``distinct T with operations``
-- implement the "easy" constructors idea; document destructors
+- implement the "easy" constructors idea
 - code generated for type information is wasteful
 - resizing of strings/sequences could take into account the memory that
   is allocated