Add additional types for eldoc

Currently the eldoc type is either `function` or `variable`:

```clj
(defn- extract-eldoc
[info]
(if-let [arglists (seq (-> info extract-arglists format-arglists))]
{:eldoc arglists :type "function"}
{:type "variable"}))
```
This means that the result users see is not particularly accurate, not to mention that the function check is pretty primitive. We should add types like `macro`, `special-form`, etc.