Added ConfigParser-based WhoConfig, implementing the spec outlined at
http://www.plope.com/static/misc/sphinxtest/intro.html#middleware-configuration-via-config-file, with the following changes:

   o "Bare" plugins (requiring no configuration options) may be specified
     as either egg entry points (e.g., 'egg:distname#entry_point_name') or
     as dotted-path-with-colon (e.g., 'dotted.name:object_id').

   o Therefore, the separator between a plugin and its classifier is
     now a semicolon, rather than a colon. E.g.:

     [plugins:id_plugin]
     use = egg:another.package#identify_with_frobnatz
     frobnatz = baz

     [identifiers]
     plugins =
       egg:my.egg#identify;browser
       dotted.name:identifier
       id_plugin