Better string mixins

[Michelle Long]

The problem with mixing in code is that one has to manually build 
code strings like:

static foreach(k; X)
    mixin("int Var"~k~" = "~k~";);

which is error prone, ugly, time consuming, and harder to read.

Instead, I propose a simple extension:

static foreach(k; X)
    mixin("int Var at k = @k;");


Here the @ simple, or whatever symbol would be best, takes the 
variable and inserts it from the outer scope as a string, 
converting it to a string if necessary.

It can only be used on such CT variables so errors should not 
exist.

If necessary, maybe

static foreach(k; X)
    @mixin("int Var at k = @k;");

or

static foreach(k; X)
    mixin(@"int Var at k = @k;");

could be used.


This avoids having to do shit like

mixin("foo("~x~", "~y~", "~z~");");

so one has

mixin("foo(@x, at y, at z);");

which translates almost directly in to standard code(one can 
simply strip the @'s).