First optimizations

This project is relatively big and very old so I didn't know where to begin. Anyway, here are few trivial optimizations:
- PNG hack for old IEs removed
- little CSS optimization
- replaced standalone contact/credits/copyright with links to php.net - I think there are no fundamental differences beetween them and it's easier to maintain only one copy for all *.php.net services
- @import replaced with normal <link> tag
- useless HTML tags from header removed

More fixes and real improvements should show up when I get local setup running and when (if?) my VCS account request will pass.