Access any mediawiki site without a family file

AutoFamily dynamically provides Family capabilities without a
special class file, using only the wiki URL.  The URL may be
only the protocol and hostname, or a URL to the API php script.

pywikibot.site.Family uses AutoFamily if it finds a URL has been
provided instead of a file path.

To use a mediawiki site without a family file, add the following
to user-config.py

family_files['mhwp'] = 'https://mh.wikipedia.org/'
usernames['whwp']['*']=u'xyz'

or

family_files['w3c'] = 'https://www.w3.org/wiki/api.php'

Bug: 70795
Change-Id: I9ad83fe996bc240fb9d5f27b866a022fccd313c0
Merge "Access any mediawiki site without a family file"