[DOCS] Sphinx -- Introduce alias detection. (apache#4954)

* [DOCS] Sphinx -- Introduce alias detection.

Background: some of our namespaces import function from another
namespace. For example tvm.te imports most of the operators from tvm.tir.

Previously we manually exclude these aliases from the doc.
However that means we can not link them by the alias name.

This PR adds a sphinx callback plugin to detect such aliases, and create a rubric block
on the button of its current docstring `Alias of the original class`.
It is done in a way so that we can refer to the generated docs.

We also fixed a few docs errors.

* Fix most of the issues

tutorials/frontend/deploy_detection.py

@@ -16,7 +16,7 @@
 # under the License.
 """
 Deploy Pretrained Vision Detection Model from Darknet on VTA
-================================================
+============================================================
 **Author**: `Hua Jiang <https://github.com/huajsj>`_
 
 This tutorial provides an end-to-end demo, on how to run Darknet YoloV3-tiny