title: How to handle 'display name' for add_object_type?
body: <p>I am using Sphinx's <code>add_object_type</code> to create a custom object <code>confval</code> for configuration file values:</p>
  
  <pre><code>add_object_type('confval', 'confval', objname='configuration value', indextemplate='pair: %s; configuration value')`
  </code></pre>
  
  <p>However I have multiple configuration files and they could have the same value.</p>
  
  <p>Consider:</p>
  
  <pre><code>..confval:  filepath
  
      Description filepath in configuration file foo.cfg
  </code></pre>
  
  <p>And</p>
  
  <pre><code>..confval:  filepath
  
      Description filepath in configuration file bar.cfg
  </code></pre>
  
  <p>I now have two filepath values.  I could make them unique by changing their names to <code>foo-filename</code> and <code>bar-filename</code> but that changes the text that is presented to the user.  </p>
  
  <p>How can I generate unique index names for the values while maintaining the text that the user sees?</p>
  
  <p>My current idea is to add an <code>index</code> option:</p>
  
  <pre><code>..confval:  filepath
      :index: foo-filepath
  
      Description filepath in configuration file foo.cfg
  </code></pre>
  
  <p>But that would require creating a directive class.  Can I do something with <code>add_object_type</code>?</p>