Best reco hits events

This addresses issues #22 (closed) and #24 (closed)

This is ready for merge into master. Although I am not sure I understand why the code style fails here on git (I updated yapf on my computer and used it to correct the code style but maybe I am missing a detail here?).

km3io/offline.py

@@ -334,7+334,7 @@
             OfflineKeys.
         """
         if self._keys is None:
             self._keys = OfflineKeys(self._file_path)
         return self._keys
 
 
@@ -378,7+378,7 @@
             if 'Head' in fobj:
                 self._header = {}
                 for n, x in fobj['Head']._map_3c_string_2c_string_3e_.items():
-                    print("{:15s} {}".format(n.decode("utf-8"),
-                                             x.decode("utf-8")))
                     self._header[n.decode("utf-8")] = x.decode("utf-8")
             else:
                 warnings.warn("Your file header has an unsupported format")