Add group get runtime function.

The format is based on [keep a changelog](http://keepachangelog.com) and this project uses [semantic versioning](http://semver.org).

## [Unreleased]

### Added

- More flexible query-based filter when listing realtime multiplayer matches.

- Runtime function to batch get groups by group ID.

### Changed

- Improved cancellation of ongoing work when clients disconnect.

- Improved validation of dispatcher broadcast message filters.

- Set maximum size of authoritative match labels to 2048 bytes.

### Fixed

- Use leaderboard expires rather than end active IDs with leaderboard resets.

- Better validation of tournament duration when a reset schedule is set.

- Set default matchmaker input query if none supplied with the request.

- Removed a potential race condition when session ping backoff triggers alongside a timed ping.

- Errors returned by InitModule hooks from Go runtime plugins will now correctly halt startup.

## [2.1.0] - 2018-10-08

### Added

  google.protobuf.Int32Value min_size = 4;

  // Maximum user count.

  google.protobuf.Int32Value max_size = 5;

  // Arbitrary label query.

  google.protobuf.StringValue query = 6;

}

// Get a list of unexpired notifications.

            "required": false,

            "type": "integer",

            "format": "int32"

          },

          {

            "name": "query",

            "description": "Arbitrary label query.",

            "in": "query",

            "required": false,

            "type": "string"

          }

        ],

        "tags": [

    print("match init context:\n" .. du.print_r(context) .. "match init params:\n" .. du.print_r(params))

  end

  local tick_rate = 1

  local label = "skill=100-150"

  local label = (params and params.label) or "skill=100-150"

  return state, tick_rate, label

end