Move main_classes to a separate folder

docs/source/main_classes/audio_processor.md

@@ -0,0 +1,25 @@
+# AudioProcessor
+
+`TTS.utils.audio.AudioProcessor` is the core class for all the audio processing routines. It provides an API for
+
+- Feature extraction.
+- Sound normalization.
+- Reading and writing audio files.
+- Sampling audio signals.
+- Normalizing and denormalizing audio signals.
+- Griffin-Lim vocoder.
+
+The `AudioProcessor` needs to be initialized with `TTS.config.shared_configs.BaseAudioConfig`. Any model config
+also must inherit or initiate `BaseAudioConfig`.
+
+## AudioProcessor
+```{eval-rst}
+.. autoclass:: TTS.utils.audio.AudioProcessor
+    :members:
+```
+
+## BaseAudioConfig
+```{eval-rst}
+.. autoclass:: TTS.config.shared_configs.BaseAudioConfig
+    :members:
+```