[suggestion] leaderboard with limited number of keypoints

[Vincentqyw]

i think there should be a leaderboard with limited keypoints, such as 500 and 1000, which will be useful for selecting keypoint for realtime SLAM.

[etrulls]

We originally did that, but opted to remove it so as not to dilute the leaderboards too much. We can reconsider this in the future, but I think SLAM datasets would be better-suited for evaluating SLAM.

[BradKML]

There are more algorithms in https://github.com/luigifreda/pyslam that is for SLAM.