Add Crossref search engine and DOAI rewrite plugin

searx/settings.yml

@@ -87,6 +87,16 @@ engines:
   - name : btdigg
     engine : btdigg
     shortcut : bt
+    
+  - name : crossref
+    engine : json_engine
+    paging : True
+    search_url : http://search.crossref.org/dois?q={query}&page={pageno}
+    url_query : doi
+    title_query : title
+    content_query : fullCitation
+    categories : science
+    shortcut : cr
 
   - name : currency
     engine : currency_convert