mixed restore_value(string str)
Decode the string representation <str> of a value back into the value
itself and return it. <str> is a string as generated by save_value().
The '#x:y' version specification of the saveformat is optional,
however the driver will assume the old format version 0 in this case.
It is strongly recommended to regard the version specification as
non-optional in newly saved values.
Introduced in LDMud 3.2.8.
LDMud 3.2.9 added the restoring of non-lambda closures, symbols,
and quoted arrays, using a new savefile format version.
LDMud 3.5.0 added the possibility to restore version 2 with its higher
save_value(E), restore_object(E), save_object(E)