Add support for nested libspecs

[borkdude]

It's not a feature I recommend to use, but it will help using several libs from the past:

borkdude@MBP2019 /tmp $ export BABASHKA_CLASSPATH=`clj -Sdeps '{:deps {cpath-clj/cpath-clj {:mvn/version "0.1.2"}}}' -Spath`
borkdude@MBP2019 /tmp $ bb -e "(require '[cpath-clj.core :as cp])"
----- Error --------------------------------------------------------------------
Type:     java.lang.IllegalArgumentException
Message:  No matching clause: [io :as io]
Location: cpath_clj/core.clj:1:1

----- Context ------------------------------------------------------------------
1: (ns cpath-clj.core
   ^--- No matching clause: [io :as io]
2:   (:require [clojure.java
3:              [io :as io]
4:              [classpath :as cp]])
5:   (:import [java.net URL URI]
6:            [java.util.jar JarFile]

----- Stack trace --------------------------------------------------------------
user - <expr>:1:1