transcribe: return all language probabilities if requested (#210)

* transcribe: return all language probabilities if requested

If return_all_language_probs is True, TranscriptionInfo structure
will have a list of tuples reflecting all language probabilities
as returned by the model.

* transcribe: fix docstring

* transcribe: remove return_all_lang_probs parameter

tests/test_transcribe.py

@@ -6,11 +6,18 @@ from faster_whisper import WhisperModel, decode_audio
 def test_transcribe(jfk_path):
     model = WhisperModel("tiny")
     segments, info = model.transcribe(jfk_path, word_timestamps=True)
+    assert info.all_language_probs is not None
 
     assert info.language == "en"
     assert info.language_probability > 0.9
     assert info.duration == 11
 
+    # Get top language info from all results, which should match the
+    # already existing metadata
+    top_lang, top_lang_score = info.all_language_probs[0]
+    assert info.language == top_lang
+    assert abs(info.language_probability - top_lang_score) < 1e-16
+
     segments = list(segments)
 
     assert len(segments) == 1