Contains functionality for cleaning ns forms.

* Eliminate :use, or :use-macro clauses.
* Sort required libraries, imports and vectors of referred symbols.
* Rewrite to favor prefix form, e.g. [clojure [string test]] instead
  of two separate libspecs.
* Raise errors if any inconsistencies are found (e.g. a libspec with more than
  one alias).
* Remove any duplication in the :require, :require-macros, :use-macros
  and :import form.
* Remove any unused required namespaces or imported classes.
* Remove any unused referred symbols.
* Prune, or remove if uneeded, the :rename clause
* Returns nil when nothing is changed, so the client knows not to do anything.

Extracts a list of imports or libspecs from an ns form.  A libspec
looks like this:

{:ns my-ns
 :as my-alias
 :refer [referred symbols here] ; or :all
 :rename {:rename :spec}
 :only [only these symbols]

 ;; rest are cljs specific
 :refer-macros [referred macros here]
 :require-macros true}

Resolve a missing symbol on the classpath.

Backports from future versions of Clojure

Search the classpath for vars and classes.