Reorganize endpoint example structure

It used to be:
<Language>
      Single Calls
            <code samples>

where all of the calls were multipart.

However, in anticipation of adding new single-part JSON calls we want to reorganize it so that we can have

<Language>
      Endpoint Examples
             Multipart Payload
                    <code samples>

so that we can eventually add "JSON Payload" to make it look like

<Language>
      Endpoint Examples
             Multipart Payload
                    <code samples>
             JSON Payload
                    <code samples>