Adopt `:autosummary:` in `torchaudio.functional` module doc (#2693)

Summary:
https://output.circle-artifacts.com/output/job/b23174d2-5cee-4ee9-be39-3228b9ae4abe/artifacts/0/docs/functional.html

<img width="1133" alt="Screen Shot 2022-09-20 at 11 19 23 AM" src="https://user-images.githubusercontent.com/855818/191152824-96c5b16c-bd38-4656-b1ae-0b58699dbd62.png">

Pull Request resolved: https://github.com/pytorch/audio/pull/2693

Reviewed By: carolineechen

Differential Revision: D39650930

Pulled By: mthrok

fbshipit-source-id: 28b5b03d21b922e37e02bfddda2bf1dea696cc18

docs/source/functional.rst

-.. role:: hidden
-    :class: hidden-section
+.. py:module:: torchaudio.functional
 
 torchaudio.functional
 =====================
 
-.. py:module:: torchaudio.functional
-
 .. currentmodule:: torchaudio.functional
 
 Functions to perform common audio operations.
 
-:hidden:`Utility`
-~~~~~~~~~~~~~~~~~
-
-amplitude_to_DB
----------------
-
-.. autofunction:: amplitude_to_DB
-
-DB_to_amplitude
----------------
-
-.. autofunction:: DB_to_amplitude
-
-
-melscale_fbanks
----------------
-
-.. autofunction:: melscale_fbanks
-
-linear_fbanks
--------------
-
-.. autofunction:: linear_fbanks
-
-create_dct
-----------
-
-.. autofunction:: create_dct
-
-mask_along_axis
----------------
+Utility
+-------
 
-.. autofunction:: mask_along_axis
+.. autosummary::
+   :toctree: generated
+   :nosignatures:
+
+   amplitude_to_DB
+   DB_to_amplitude
+   melscale_fbanks
+   linear_fbanks
+   create_dct
+   mask_along_axis
+   mask_along_axis_iid
+   mu_law_encoding
+   mu_law_decoding
+   apply_codec
+   resample
+   loudness
+
+
+Filtering
+---------
 
-mask_along_axis_iid
+.. autosummary::
+   :toctree: generated
+   :nosignatures:
+
+   allpass_biquad
+   band_biquad
+   bandpass_biquad
+   bandreject_biquad
+   bass_biquad
+   biquad
+   contrast
+   dcshift
+   deemph_biquad
+   dither
+   equalizer_biquad
+   filtfilt
+   flanger
+   gain
+   highpass_biquad
+   lfilter
+   lowpass_biquad
+   overdrive
+   phaser
+   riaa_biquad
+   treble_biquad
+
+Feature Extractions
 -------------------
 
-.. autofunction:: mask_along_axis_iid
-
-mu_law_encoding
----------------
-
-.. autofunction:: mu_law_encoding
-
-mu_law_decoding
----------------
-
-.. autofunction:: mu_law_decoding
-
-apply_codec
------------
-
-.. autofunction:: apply_codec
-
-resample
---------
-
-.. autofunction:: resample
-
-loudness
---------
-
-.. autofunction:: loudness
-
-
-:hidden:`Filtering`
-~~~~~~~~~~~~~~~~~~~
-
-
-allpass_biquad
---------------
-
-.. autofunction:: allpass_biquad
-
-band_biquad
------------
-
-.. autofunction:: band_biquad
-
-bandpass_biquad
----------------
-
-.. autofunction:: bandpass_biquad
-
-bandreject_biquad
------------------
-
-.. autofunction:: bandreject_biquad
-
-bass_biquad
------------
-
-.. autofunction:: bass_biquad
-
-biquad
-------
-
-.. autofunction:: biquad
-
-contrast
---------
-
-.. autofunction:: contrast
-
-dcshift
--------
-
-.. autofunction:: dcshift
-
-deemph_biquad
+.. autosummary::
+   :toctree: generated
+   :nosignatures:
+
+   vad
+   spectrogram
+   inverse_spectrogram
+   griffinlim
+   phase_vocoder
+   pitch_shift
+   compute_deltas
+   detect_pitch_frequency
+   sliding_window_cmn
+   compute_kaldi_pitch
+   spectral_centroid
+
+Multi-channel
 -------------
 
-.. autofunction:: deemph_biquad
-
-
-dither
-------
-
-.. autofunction:: dither
+.. autosummary::
+   :toctree: generated
+   :nosignatures:
 
-equalizer_biquad
-----------------
+   psd
+   mvdr_weights_souden
+   mvdr_weights_rtf
+   rtf_evd
+   rtf_power
+   apply_beamforming
 
-.. autofunction:: equalizer_biquad
-
-filtfilt
---------
-
-.. autofunction:: filtfilt
-
-flanger
--------
-
-.. autofunction:: flanger
-
-gain
+Loss
 ----
 
-.. autofunction:: gain
-
-highpass_biquad
----------------
+.. autosummary::
+   :toctree: generated
+   :nosignatures:
 
-.. autofunction:: highpass_biquad
+   rnnt_loss
 
-lfilter
--------
-
-.. autofunction:: lfilter
-
-lowpass_biquad
---------------
-
-.. autofunction:: lowpass_biquad
-
-overdrive
----------
-
-.. autofunction:: overdrive
-
-phaser
+Metric
 ------
 
-.. autofunction:: phaser
-
-riaa_biquad
------------
-
-.. autofunction:: riaa_biquad
-
-treble_biquad
--------------
-
-.. autofunction:: treble_biquad
-
-:hidden:`Feature Extractions`
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-:hidden:`vad`
--------------
-
-.. autofunction:: vad
-
-:hidden:`spectrogram`
----------------------
-
-.. autofunction:: spectrogram
-
-:hidden:`inverse_spectrogram`
------------------------------
-
-.. autofunction:: inverse_spectrogram
-
-:hidden:`griffinlim`
---------------------
-
-.. autofunction:: griffinlim
-
-:hidden:`phase_vocoder`
------------------------
-
-.. autofunction:: phase_vocoder
-
-:hidden:`pitch_shift`
----------------------
-
-.. autofunction:: pitch_shift
-
-:hidden:`compute_deltas`
-------------------------
-
-.. autofunction:: compute_deltas
-
-:hidden:`detect_pitch_frequency`
---------------------------------
-
-.. autofunction:: detect_pitch_frequency
-
-:hidden:`sliding_window_cmn`
-----------------------------
-
-.. autofunction:: sliding_window_cmn
-
-:hidden:`compute_kaldi_pitch`
------------------------------
-
-.. autofunction:: compute_kaldi_pitch
-
-:hidden:`spectral_centroid`
----------------------------
-
-.. autofunction:: spectral_centroid
-
-:hidden:`Multi-channel`
-~~~~~~~~~~~~~~~~~~~~~~~
-
-psd
----
-
-.. autofunction:: psd
-
-mvdr_weights_souden
--------------------
-
-.. autofunction:: mvdr_weights_souden
-
-mvdr_weights_rtf
-----------------
-
-.. autofunction:: mvdr_weights_rtf
-
-rtf_evd
--------
-
-.. autofunction:: rtf_evd
-
-rtf_power
----------
-
-.. autofunction:: rtf_power
-
-apply_beamforming
------------------
-
-.. autofunction:: apply_beamforming
-
-:hidden:`Loss`
-~~~~~~~~~~~~~~
-
-rnnt_loss
----------
-
-.. autofunction:: rnnt_loss
-
-:hidden:`Metric`
-~~~~~~~~~~~~~~~~
-
-edit_distance
--------------
+.. autosummary::
+   :toctree: generated
+   :nosignatures:
 
-.. autofunction:: edit_distance
+   edit_distance