1. Since the customizable table cloning function may be useful for
other purposes than just making Chronomancy clones, I moved it to
engine/class.lua and renamed it cloneCustom(). It works like
cloneFull(), but allows specifying a table of keys/values to skip or
replace in the clone table.

If desired, I could instead just modify cloneFull() to have an optional
parameter for the "alt_nodes" table, but I didn't want to mess with it
without permission. There could be a conditional statement to pick
between two different recursive functions so the optional param doesn't
impact performance, if that's a concern.

2. Updated comments for cloneFull() and related functions for clarity.
The comment originally said it returns the clone and the number of
objects cloned, but it actually only returns the clone. I think the
comment may have been copied from somewhere else and not updated.

3. Renamed the "t" param from cloneFull() to "post_copy" to be more
descriptive and to be consistent with cloneCustom(). This has no
functional impact.

4. Significantly expanded the number of properties which are skipped
when making Chronomancy clones of an actor. Hopefully this will improve
performance and maybe even help with the memory leak. I didn't see any
errors during brief testing, but it probably merits more testing.

Changed Arcane Combat's description generator to use table.concat, to
avoid making temporary string objects that need garbage collection.

Adds more zone-wide effects in. About half of them explain special level mechanics, the rest are just for flavour or some minor gameplay spice.

I just remembered why I originally designed it this way: We only want
to skip if neither 'k' nor 'v' is specified in alt_nodes since we want
to allow substituting user-specified values for either.

Fix 1: Improve cloning function

Previously, makeParadoxClone() temporarily cleared the actor's
particles and main inventory so that they wouldn't be copied by
cloneFull() when making Warden's Call clones. However, this resulted
in some players losing their inventory, probably due to some race
condition during lag caused by the Warden's Call memory leak.

Now, makeParadoxClone() has its own recursive table cloning function
with options for skipping specific nodes or assigning them a different
value from the source table. This way, we can clone an actor without
modifying that actor's table.

Fix 2: Create cleanup function for Warden's Call

Added a basic cleanup function for Warden's Call clones. Currently, it
just makes sure they're dead and replaces references in timed effects
with references to the player, so the clones can be freed by the
garbage collector. More features will likely be added as I find other
causes of the memory leak.

NOTE: These changes don't fix the memory leak. It may help a little,
but that issue needs more investigation.

It's probably worth pushing these changes back to v1.3.X in a minor
update to fix the issue with missing player inventory. Completely
fixing the memory leak may take a while.

Simplified support of double shields by enhancing actor:hasShield()

Sometiems, rarely, a special room will appear in the Infinite Dungeon to let you access the Item's Vault (if you have it active and are a donator)