Remove python function wrapper.

[hjchen2]

移除python中的function wrapper，并解决builtin function添加doc的问题。

[hjchen2]

禁止pybind自动生成doc

[doombeaker]

这个 F 名字空间，其实作用是对应了 torch 中的 torch._C 吧？
我们是未来会改成 _C 吗？

[hjchen2]

目前感觉没太大必要，和torch的_C也不是完全对应。torch的接口导出比较分散，有些直接导出到torch，有些是torch._C，我们都统一到F

[doombeaker]

好的。

[github-actions]

CI failed, removing label automerge

[github-actions]

CI failed, removing label automerge

[github-actions]

CI failed, removing label automerge

[github-actions]

Speed stats:

GPU Name: GeForce GTX 1080 

PyTorch resnet50 time: 140.4ms (= 7021.5ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 128.3ms (= 6415.7ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
Relative speed: 1.09 (= 140.4ms / 128.3ms)

PyTorch resnet50 time: 84.6ms (= 4227.5ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 74.5ms (= 3725.0ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
Relative speed: 1.13 (= 84.6ms / 74.5ms)

PyTorch resnet50 time: 60.2ms (= 3011.1ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 47.8ms (= 2390.2ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
Relative speed: 1.26 (= 60.2ms / 47.8ms)

PyTorch resnet50 time: 49.8ms (= 2488.0ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 40.6ms (= 2031.0ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
Relative speed: 1.22 (= 49.8ms / 40.6ms)

PyTorch resnet50 time: 42.8ms (= 2138.3ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 41.3ms (= 2063.8ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
Relative speed: 1.04 (= 42.8ms / 41.3ms)