bump release to 1.3.3
add prebuilt userscripts
Add comment to README for v1.3.3
Update README.md
bump version number to v1.3.3.3 for hotfix release

Jumping to v1.3.3.3 even though the master branch is still sporting v1.3.3
because the Firefox extension release used v1.3.3.1 and the Chrome store
extension release is past that at v1.3.3.2.
add prebuilt userscript for v1.3.3.3