Some small changes

alternate: add "print error", "execute SQL", and fix double start bug
rss_reader: retrieve only the last error instead of all errors
post: a typo
sql: prettier output
Publish to multiple groups -- the very first
Modify lots in index

1. move auth to auth.php
2. fix some bugs in group
Publish to multiple groups almost done

Rewrite users.php using static member functions
Lots of changes, especially using OOP in most files