Removed conditionals for includes

Removed conditional checks for admin includes.
Added 'Includes' section

Added a section for file includes at the top of the main plugin file.
Removed $post_id

Removed $post_id from global declaration as it is unused in this
function.
Added 'multiple-authors' conditional

Added a conditional check to run certain code depending on whether the
‘multiple-authors’ plugin option is enabled.
Moved code

Moved code to Includes section at the top of the file.
Added mention of Co-Authors Plus

Added credit to the WordPress plugin Co-Authors Plus since I’m using
some code from that plugin in this one.
Renamed Class

Renamed the class since it is no longer just for admin, but the entire
multiple authors process.
Added new action hook

Added another ‘init’ action hook to load certain code late in the init
process.
Created function

Created function ‘cc_author_multiauthors’ which calls constructor.
Created main init function

Created the function for the main init call.
Late init function

Created the function for late-execution init code.
Renamed function

Renamed function for simpler use.