Adds LabeledSentence to gensim.models.doc2vec (for backward compa…

…tibility). Fix piskvorky#1886 (piskvorky#1891)

gensim/models/doc2vec.py

@@ -70,6 +70,7 @@
 from gensim.models.base_any2vec import BaseWordEmbeddingsModel
 from gensim.models.keyedvectors import Doc2VecKeyedVectors
 from types import GeneratorType
+from gensim.utils import deprecated
 
 logger = logging.getLogger(__name__)
 
@@ -247,6 +248,12 @@ def __str__(self):
         return '%s(%s, %s)' % (self.__class__.__name__, self.words, self.tags)
 
 
+# for compatibility
+@deprecated("Class will be removed in 4.0.0, use TaggedDocument instead")
+class LabeledSentence(TaggedDocument):
+    pass
+
+
 class Doctag(namedtuple('Doctag', 'offset, word_count, doc_count')):
     """A string document tag discovered during the initial vocabulary
     scan. (The document-vector equivalent of a Vocab object.)