[to #41999503] refine doc and requirements for linux and mac

1. refine quick start and pipeline doc
2. remove tf pytorch easynlp from requirements
3. lazy import for torch and tensorflow
4. test successfully on linux and mac intel cpu
5. update api doc

Link: https://code.alibaba-inc.com/Ali-MaaS/MaaS-lib/codereview/8882373

docs/source/api/maas_lib.pipelines.audio.rst

@@ -0,0 +1,7 @@
+maas\_lib.pipelines.audio package
+=================================
+
+.. automodule:: maas_lib.pipelines.audio
+   :members:
+   :undoc-members:
+   :show-inheritance:

docs/source/api/maas_lib.trainers.nlp.rst

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+maas\_lib.trainers.nlp package
+==============================
+
+.. automodule:: maas_lib.trainers.nlp
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+Submodules
+----------
+
+maas\_lib.trainers.nlp.sequence\_classification\_trainer module
+---------------------------------------------------------------
+
+.. automodule:: maas_lib.trainers.nlp.sequence_classification_trainer
+   :members:
+   :undoc-members:
+   :show-inheritance:

docs/source/api/maas_lib.trainers.rst

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+maas\_lib.trainers package
+==========================
+
+.. automodule:: maas_lib.trainers
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+Subpackages
+-----------
+
+.. toctree::
+   :maxdepth: 4
+
+   maas_lib.trainers.nlp
+
+Submodules
+----------
+
+maas\_lib.trainers.base module
+------------------------------
+
+.. automodule:: maas_lib.trainers.base
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+maas\_lib.trainers.builder module
+---------------------------------
+
+.. automodule:: maas_lib.trainers.builder
+   :members:
+   :undoc-members:
+   :show-inheritance: