add HSTS header

since this service is intended to be HTTPS only, HSTS is another way of helping to ensure that.
Removed the old method of output buffering, just don't do that anymore
Moved the cleanup to after the moment that content is returned to the user, makes it a bit faster
Made the system XHTML 1.0 Transitional compliant
fixed typo
Merge branch 'master' of https://github.com/Cybertinus/6paster into Cybertinus-master
Merge branch 'Cybertinus-master'
Merge branch 'master' of https://github.com/dunamis/6paster