Closes: #5849

Add autodoc_default_options

Plugins can resolve imported members for viewcode

The "any" and "func" roles now accepts full function declarations.

Fixes #1552

As the previous commit explains, it is now possible to specify arguments
to the global options in config files. This means that we can now include
the `exclude-members` option in this global configuration.

Previously, there was no point including this option because it makes no
sense without arguments. Including this option means users have the
flexibility of explicitly including which special methods they want using
(e.g.):

  :special-members: __init__, __iter__

or explicitly excluding which special-members (or other members) they want
using (e.g.):

  :exclude-members: __weakref__, __hash__

Previously, users could specify a *list* of flags in their config files.
The flags were directive names that would otherwise be present in the
.rst files. However, as a list, it was not possible to specify values
to those flags, which *is* possible in .rst files.

For example, in .rst you could say

  :special-members: __init__, __iter__

And this would cause autodoc to generate documents for these methods that
it would otherwise ignore.

This commit changes the config option to instead accept a dictionary.
This is a dictionary whose keys can contain the same flag-names as before,
but whose values can contain the arguments as seen in .rst files.

The old list is still supported, for backwards compatibility, but the data
is transformed into a dictionary when the user's config is loaded.