generate Python API document automatically

[njzjz]

preview: https://explore-deepmd.njzjz.win/en/latest/api_py/api_py.html

[codecov-commenter]

Codecov Report

Merging #998 (6818c1e) into devel (f3b08b3) will increase coverage by 7.81%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            devel     #998      +/-   ##
==========================================
+ Coverage   75.46%   83.27%   +7.81%     
==========================================
  Files          85      118      +33     
  Lines        6794     9980    +3186     
==========================================
+ Hits         5127     8311    +3184     
- Misses       1667     1669       +2     

Impacted Files	Coverage Δ
source/lib/tests/test_pair_tab.cc	100.00% <0.00%> (ø)
source/lib/tests/test_prod_virial_a.cc	100.00% <0.00%> (ø)
source/api_cc/tests/test_deepdipole.cc	100.00% <0.00%> (ø)
source/lib/tests/test_coord.cc	100.00% <0.00%> (ø)
source/lib/tests/test_neighbor_list.cc	100.00% <0.00%> (ø)
source/api_cc/tests/test_deeppot_model_devi.cc	100.00% <0.00%> (ø)
source/lib/tests/test_prod_virial_grad_a.cc	100.00% <0.00%> (ø)
source/lib/tests/test_main.cc	100.00% <0.00%> (ø)
...ource/lib/tests/test_soft_min_switch_force_grad.cc	100.00% <0.00%> (ø)
source/lib/tests/test_map_aparam.cc	100.00% <0.00%> (ø)
... and 23 more

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[njzjz]

What do you think better, put modules (e.g. deepmd.descriptor.hybrid and deepmd.descriptor.loc_frame) in a single page (deepmd.descriptor), or in the separated pages?