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.

No se nombran archivos, pruebas ni puntos de entrada. Empieza por inventariar los docstrings del proyecto y comparar su salida renderizada en pydoc con las convenciones de Sphinx; se considera terminado cuando haya reglas de formato acordadas para los parámetros y valores de retorno recurrentes, además de docstrings reescritos que sigan siendo utilizables en pydoc.