Syntax: OVERLOAD keyword INTEGER

   Allow "keyword" (in lowercase) to be used as a macro name if
integer is non-zero. For example "overload set 1 overload define 1
macro set { DEFINE } macro define { SET }" would interchange the
meanings of the "SET" and "DEFINE" commands. The uppercase forms of
the keywords retain their usual meanings. Beware that, if you overload
help, "set help x help_string" won't work.