Container::register() is chainable and checks the alias.

Container::remove() removes the instance too.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5553 2fea6a4d-a838-0410-917b-93a53c48e9d2
Update documentation.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5554 2fea6a4d-a838-0410-917b-93a53c48e9d2
Txp::getContainer() to public.

Exposes the current container through the factory interface.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5555 2fea6a4d-a838-0410-917b-93a53c48e9d2