SLEEP expression

   Synopsis:
      Pauses execution of the Axbasic script

   Notes:
      When the Axbasic script is being run from within an Axmud task, execution 
         can be suspended with statements such as PAUSE, SLEEP, BREAK and 
         WAITTRIG.
      SLEEP causes execution of the script to halt for the specified number of
         seconds. Execution resumes when the parent task unpauses itself.
      The expression must evaluate to a positive integer.
      The PAUSE and SLEEP statements behave in exactly the same way.

   Requires:
      If the script is not being run as a task, the SLEEP statement is ignored
         (and no error message is generated). Execution continues with the next
         statement.
         
   Examples:
      SEND "drop treasure"
      SLEEP 3
      SEND "bury treasure"
