I didn't add standard Lua require() because I've always been
afraid of it. I'm not sure we can guarantee which files it
will read (or not read).
Instead, here is a custom implementation. It should work more
or less the same and allow for more modular code.
For backwards compatibility reasons, all of the lua files in
the base mod folder will be loaded as in the past. Aka one at
a time and alphabetically.
However, now coop will look for Lua files in subdirectories
and will load them in when another Lua file calls require().
The file search order is more reasonable than normal Lua
require(). It will first look for files relative to the
currently running script. If there is no matching relative
file, it will pick from any Lua file that is in any of the
mod's subdirectories.
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Co-authored-by: MysterD <myster@d>
