Make docstrings to be nice with pydoc

In some doc-strings we use formatting rules specific to Sphinx, but which make the interactive help (pydoc) to look bad.

This issue is about:

• defining how we should write some recurrent stuff, like documenting input parameters and return values.
• rewrite the doc-strings so they look fine on pydoc, even if that means losing some features with Sphinx, like cross references.

Note. If we had the resources, we would do like Python does, and document things twice: once in the doc-strings and a feature rich version in the rst files. But in any case the doc-strings must be usable with pydoc, so lets start with that.

未指定任何文件、测试或入口点。首先盘点项目中的 docstrings，并将它们在 pydoc 中的渲染输出与 Sphinx 约定进行比较；完成的标准是：已就重复出现的参数和返回值制定一致的格式规则，并且重写后的 docstrings 仍可在 pydoc 中使用。