Add Danish rules (#135)

* create Danish rules

Sample words:

næste => naeste
læring => laering
søster => soester
børn => boern
år => aar
måske => maaske
allé => alle
én => en

* add test for Danish rules

* add Danish rules to RuleProvider

Author: johnnyfekete

Diff for: Resources/rules/danish.json

@@ -0,0 +1,10 @@
+{
+    "Æ": "Ae",
+    "æ": "ae",
+    "Ø": "Oe",
+    "ø": "oe",
+    "Å": "Aa",
+    "å": "aa",
+    "É": "E",
+    "é": "e"
+}

Diff for: src/RuleProvider/DefaultRuleProvider.php

@@ -303,6 +303,17 @@ class DefaultRuleProvider implements RuleProviderInterface
     'ů' => 'u',
     'ž' => 'z',
   ),
+  'danish' =>
+  array(
+    'Æ' => 'Ae',
+    'æ' => 'ae',
+    'Ø' => 'Oe',
+    'ø' => 'oe',
+    'Å' => 'Aa',
+    'å' => 'aa',
+    'É' => 'E',
+    'é' => 'e',
+  ),
   'default' => 
   array (
     '°' => '0',

Diff for: tests/SlugifyTest.php

@@ -155,6 +155,7 @@ public function customRulesProvider()
             ['azerbaijani', 'əöüğşçı', 'eougsci'],
             ['azerbaijani', 'Fərhad Səfərov', 'ferhad-seferov'],
             ['croatian', 'Č Ć Ž Š Đ č ć ž š đ', 'c-c-z-s-dj-c-c-z-s-dj'],
+            ['danish', 'Æ æ Ø ø Å å É é', 'ae-ae-oe-oe-aa-aa-e-e'],
         ];
     }