anchor.diff:  Modifies the member position in all the rankings in which was participating.  
   The data needed to register the member is the following:
   
  -- score ... the score to be applied to all rankings
  +- **score** ... the score to be applied to all rankings
  +- **collection** ... the [collection of rankings] (#ranking_collections) to be updated 
   
   + Parameters
       + mbr (string)... the id of the member
  
positive.code: 
  # plyrhub-ranking
  Set of resources that allow the management and querying of rankings.
  
  # Group Ranking Information
     
  ## Rankings Inventory [/rankings(?platform=web&offset=0&limit=5)]
  ### List all the available rankings [GET]
  Returns the list of available rankings. 
  The method can be parameterized to return specific textual values for a certain platform (see <a id="System Platfomrs">System Platforms</a>), 
  and also can paginate the results (see <a id="Pagination Rules">Pagination Rules</a>).   
  The returned data provide the following information:
  
  - rnk ... the id of the ranking
  - name ... the name of the ranking
  - desc ... a long description of the ranking
  - members ... an aproximate number of members taken into account in the ranking
  
  + Parameters
      + platform (optional, string) ... The id of one of the available platforms
      + offset (optional, integer) ... The offset to apply in the pagination process
      + limit (optional, integer) ... The number of items to return 
  
  
negative.code: + Response 200 (application/json)
  
          {
              "rankings": [
                  {
                      "ranking": {
                          "rnk": "rAllUsers",
                          "name": "All Users",
                          "desc": "This ranking takes into account all users in the platform",
                          "members": 5000000
                      },
                      "position": {
                          "pos": "12456",
                          "score": "3455677"
                      }
                  },
                  {
                      "ranking": {
                          "rnk": "rNewYork",
                          "name": "New York Users",
                          "desc": "This ranking takes into account all users in NYC",
                          "members": 5000000
                      },
                      "position": {
                          "pos": "12456",
                          "score": "1455677"
                      }
                  }
              ]
          }
  