Ensure `(defn- as-path)` form is fully declared.

While Clojure 1.4 silently accepts the incomplete form:
```clojure
(defn- as-path
  "Ensure path")
```

Clojure 1.5 is more particular, causing failure when requiring the `org.bovinegenius.exploding-fish` namespace:
```
user> (require 'org.bovinegenius.exploding-fish :reload-all)
IllegalArgumentException Parameter declaration missing  clojure.core/assert-valid-fdecl (core.clj:6716)
```

`as-path` was fully re-declared in a `letfn` inside `resolve-path`, so I've simply extracted the internal declaration
and inserted it in the top-level `as-path`, making the top-level form complete.
Merge pull request #7 from rheimbuch/fix-incomplete-as-path

Ensure `(defn- as-path)` form is fully declared for Clojure 1.5 compatibility.