Updates for CMS 18 & beyond

This PR:
Replaces references to the 17th edition with the 18th
Cuts the generic pronoun line (now redundant with 5.51/5.266)
Cuts the “acronyms should generally be spelled out…” line (now redundant with 10.3) 
Adds the BCC title capitalization notes from our 10/30 team meeting to the Cover Copy section
Makes the Word List more manageable:
--Adds Word List description
--Moves acronyms that don’t need expansion to Abbreviations/Acronyms 
--Moves terms to avoid from Word List to the “To avoid unintentional bias” blurb
--Cuts “Twitter user” from Word List now that it’s X and also inappropriate (I don’t feel a replacement to X user is necessary, but can add if it starts to come up). Leaves alternatives to “tweet out” and conventions.
Consolidates footnote guidance (it just felt really clunky to me with all the divs!) and divides it into the Citation and Punctuation sections
Adds an xref to Formatting Code in Word to the Considering Electronic Formats
Alphabetizes many lists and subsections
Fixes the broken Gen AI xref
Removes bold from old changes

And will definitely require some cleanup when pushed. I'll make sure to check for errors when I can see it without all the markup.

Author: katherinetozer