empty the diffedList and downloadedList. now it's ready to use.

edit the index.html to ensure the text display correctly.
function to-do list:
1. Check the last update time so that we can keep the local saved
revision documents up-to-date
2. The image export function only works at SVG to SVG mode. Need to work
out how to export image as PNG/JPEG. Meanwhile, the SVG export file is
huge, in some cases. Need to consider how to do the compression.
Deployment to-do:
find a server and domain name to deploy it as demo for users to test.
Delete /bin and the font file.