Add w2v->compare_to parameter and use for count-based delta calcs

Change-Id: Ic53cbc5b3984659b3ebfa6c8ad30fd42850a9fc9
diff --git a/example.conf b/example.conf
index 4991015..ddc1d2f 100644
--- a/example.conf
+++ b/example.conf
@@ -14,6 +14,7 @@
 
   w2v => {
     vecs => "example-models/wpd19_10000/wpd19_10000.vecs",
+    # compare_to => "https://corpora.ids-mannheim.de/openlab/derekovecs", # compare results to this derekovecs instance
     # korap_url => "https://korap.ids-mannheim.de"
   },