Lag after holding down scroll key

[justinpombrio]

If you hold down j for a while on a very long Json document (and have a fast key-repeat), it will continue to scroll even after you release the key. We should instead behave more like Vim, which stops scrolling as soon as you release the key.

Presumably Crossterm is queuing the events, and then we're processing them one at a time, long after they occurred.