canvas playback rate

An extensions that enhances the Canvas learning experience for SJTUers.

At the origin canvas website, when users using the vShare to review the record of lesson, users can't use the space to pause and play video and left and right arrow also can't control the rate. It's inconvenience for learning.

As far, I make an easy tool for learning.

By canvas playback rate, user can freely set the playback rate, even if users want to a decimal fraction.
At the same time, users also can use space and left and arrow key to control video player.