Improve pretty-printing of namespaces

This makes the pretty-printed namespace form more in line with the
clojure style guide.

Specifically we go from:

```
(ns foo.bar
  (:require [this.library :as lib]))
```

To:

```
(ns foo.bar
  (:require
    [this.library :as lib]))
```

This commit closes clojure-emacs/clj-refactor.el#459

CHANGELOG.md

@@ -2,9 +2,11 @@
 
 ## Unreleased
 
+* [clojure-emacs/clj-refactor.el#459](https://github.com/clojure-emacs/clj-refactor.el/issues/459): `clean-ns` should conform to the style guide: `(:require` in the ns form should be followed by a newline.
 * [#294](https://github.com/clojure-emacs/refactor-nrepl/pull/294): Properly skip uneval nodes when looking for the first/last sexp
 * From now on, if you set the `clojure.tools.namespace.repl/refresh-dirs`, files outside said `refresh-dirs` won't be analyzed, resulting in safer, more efficient analysis.
 
+
 ## 2.5.1 (2021-02-16)
 
 ### Bugs fixed

src/refactor_nrepl/ns/pprint.clj

@@ -36,7 +36,7 @@
 
 (defn pprint-require-form
   [[_ & libspecs]]
-  (print "(:require ")
+  (print "(:require\n")
   (dorun
    (map-indexed
     (fn [idx libspec]

test/resources/artifacts_pprinted

@@ -1,13 +1,14 @@
 (ns refactor-nrepl.artifacts
-  (:require [clojure
-             [edn :as edn]
-             [string :as str]]
-            [clojure.data.json :as json]
-            [clojure.java.io :as io]
-            [nrepl
-             [middleware :refer [set-descriptor!]]
-             [misc :refer [response-for]]
-             [transport :as transport]]
-            [org.httpkit.client :as http]
-            [refactor-nrepl.externs :refer [add-dependencies]])
+  (:require
+   [clojure
+    [edn :as edn]
+    [string :as str]]
+   [clojure.data.json :as json]
+   [clojure.java.io :as io]
+   [nrepl
+    [middleware :refer [set-descriptor!]]
+    [misc :refer [response-for]]
+    [transport :as transport]]
+   [org.httpkit.client :as http]
+   [refactor-nrepl.externs :refer [add-dependencies]])
   (:import java.util.Date))

test/resources/ns1_cleaned_and_pprinted

@@ -8,13 +8,11 @@
    :name com.domain.tiny
    :extends java.lang.Exception
    :methods [[binomial [int int] double]])
-  (:require [clojure data edn xml
-             [instant :as inst :reload true]
-             [pprint :refer [cl-format formatter get-pretty-writer]]
-             [string :refer :all :reload-all true]
-             [test :refer :all]
-             [walk :refer [postwalk prewalk]]]
-            clojure.test.junit)
+  (:require
+   [clojure data edn xml
+    [pprint :refer [cl-format formatter get-pretty-writer]]
+    [walk :refer [postwalk prewalk]]]
+   clojure.test.junit)
   (:import [java.io Closeable FilenameFilter PushbackReader]
            [java.util Calendar Date Random]
            [refactor.nrepl SomeClass$InnerClass$InnerInnerClassOne SomeClass$InnerClass$InnerInnerClassTwo]))

test/resources/ns_with_gen_class_methods_meta_clean.clj

@@ -4,4 +4,5 @@
              ^:test [bar [String] String]
              ^{:other "text"} [baz [String] String]]
    :name Name)
-  (:require [clojure.pprint :refer [fresh-line]]))
+  (:require
+   [clojure.pprint :refer [fresh-line]]))

test/resources/ns_with_lots_of_meta_clean.clj

@@ -6,4 +6,5 @@
              ^:test [bar [String] String]
              ^{:other "text"} [baz [String] String]]
    :name Name)
-  (:require [clojure.pprint :refer [fresh-line]]))
+  (:require
+   [clojure.pprint :refer [fresh-line]]))