Introduce Chars

This improves the implementation by introducing a class to manage the characters

src/ilp_keyboard_layout_optimization/receive_data.py

@@ -142,9 +142,9 @@ class CharProbs:
 
 if __name__ == "__main__":
     CharProbs(
-        ("a", "b", "c"),
+        None,
         "http://www.ids-mannheim.de/fileadmin/kl/derewo/"
         "DeReChar-v-uni-204-a-c-2018-02-28-1.0.csv",
         "http://practicalcryptography.com/media/cryptanalysis/files/"
-        "icelandic_bigrams.txt",
+        "german_bigrams.txt",
     )