gc: destructors is beginning to work (#10483)

* kochdocs.nim: code cleanup
* docgen: nicer indentation
* parser.nim: code cleanup
* fixes #10458
* make tests green again
* make =destroy mixins
* gc:destructors: produced C code is almost working
* --gc:destructors simple program compiles (but leaks memory)
* gc:destructors make examples compile in C++ mode
* destructors: string implementation bugfixes
* strs.nim: minor code cleanup
* destructors: builtin seqs are beginning to work
* remove debugging helpers

compiler/ast.nim

@@ -1352,7 +1352,6 @@ proc copySym*(s: PSym): PSym =
   result = newSym(s.kind, s.name, s.owner, s.info, s.options)
   #result.ast = nil            # BUGFIX; was: s.ast which made problems
   result.typ = s.typ
-  result.id = getID()
   when debugIds: registerId(result)
   result.flags = s.flags
   result.magic = s.magic