Fix: "[]" for primitive invar types;
Fix: string to integer;
Change: return value of a few string methods.
Change: string methods chop(), trim(), replace() and change() to invar methods;
Remove: string methods resize(), clear(), insert() and erase();
Move: std.string(), std.array(), std.list() and std.map() to the corresponding types;
Fix: a couple of minor bugs in the handling of type holders and type specialization.