Release 1.57.0
Remove beta notes
Another thing to remove.
Stub release notes for 1.58.0
Update site to use new build sub-site.

Updated redirects, removed now unused filter, added some notes about
directories that need to be set up.
Remove some more unused filters.
Remove remaining uses of old css directory.
Remove the old style sheets.

Left behind csshover3.htc as there were some remaining uses that I
missed before.