mixin identifiers concept

[mesni]

```d
static foreach(name; ["boo", "foo"]){
     string file_#name = readText(name~".txt");
     string file_#name#_info = readText(name~".meta");
     auto ##name = file_#name#_info.parseInfoFile;
}

writeln(file_boo);
writeln(boo);
writeln(file_foo_info);
```
To make it easier to read/write code in D, I would introduce new 
mixins. These mixins can only represent identifiers. Also, the 
advantage of such mixins, the parser and semantic analysis will 
be able to detect some errors before the code is completely 
"opened". Also, I think they can speed up compilation.