alphabetization in handbook "hides" some tlak sessions.

[jeisner]

I'm not sure whether aclpub2 produces the conference handbook, but it probably should -- adopting best practices from past handbooks.

Here were a couple of issues with the ACL2023 handbook:

• No page headers -- see #155
• Within each timeslot, I recommend that all talk sessions should be listed at the start, so that attendees can easily circle specific talks they want to be at. In this handbook, the sessions were listed strictly alphabetically, so "Posters" fell in the middle of the listing. I was unaware of a few of the talk sessions because they fell alphabetically after the super-long "Posters" section!