restler grammar should support fuzzable elements for format: date-span and uri

For the following Swagger defined properties:

          "timeSpan": {
              "type": "string",
              "description": "A string which is interpreted as a TimeSpan",
              "format": "date-span",
              "nullable": true
            }

          "targetUrl": {
            "type": "string",
            "format": "uri",
            "nullable": true
          }

Currently, these are compiled to restler_fuzzable_string.

It should instead be restler_fuzzable_date_span and restler_fuzzable_uri.