…ill help to construct one parsed docstring from several parts.

We mimic the Signature.__str__ method for the implementation but instead of returning a str we return a ParsedDocstring, which is far more convenient.

This change fixes #801:
- Parameters html are divided into .sig-param spans.
- When the function is long enought an extra CSS class .expand-signature is added to the parent function-signature.
- The first parameter 'cls' or 'self' of (class) methods is marked with the 'undocumented' CSS class, this way it's clearly not part of the API.
- Add some CSS  to expand the signature of long functions when they have the focus only.

…miza a little the _colorize_signature() function.

… docstrings they only update the local to_stan() method dynamically.

…w parsed docstrings they only update the local to_stan() method dynamically."

This reverts commit eca5ced.

…class.

Introduce ParsedDocstring.to_text().

…s when overloads are overwhelming... This probably requires some more tweaks but it's still better than showing everything at once.

…t try to do such things either...

Fix some cyclic imports issue as a drive-by change: model.Documentable was uncessarly runtime imported inside restructuredtext and epydoc parsers.

also remove the summary caching on the parsed docstring side, this is unnecessary because it's already cahed in the documentable.

…of a string.

A some annotation.

… long annotations.

…nnotation is ambiguous (pydoctor is not a checker).

Get rid of ParsedDocstring.with_linker() this API did not make sens and was rather an anti-pattern.

Replace that with a new parameter of colorize_pyval(is_annotation: bool). obj_reference nodes can now be created with the attribute 'is_annotation' in which case they will be resolved a little bit differently.

…o 801-signature-spans