Feature request: as-> highlighting

I was recently having to write a rather complex set of threading code with `as->` and it occurred to me that it would be useful if in an `as->` sexp, we set the font-face of the name of the bound value to a different font face than normal so that it stood out a bit.

Example:

Instead of

``` clojure
(as-> {:cat 5} x
(reduce some-fn
x
(mapcat someother-fn some-val))
(assoc x :dog 27)
(map weird-fn x)
(map x some-coll))
```

font-locked `x` with some special font-face so we can make it stand out to make it easier to quickly parse out this information.

I would consider this to be very low priority, but might be a nice to have.