refined library i/f and improved performance

refined library i/f and improved performance

 Library changes
   readproc
    . added readeither to more efficiently
      fill both process and thread proc_t
    . added readproctab3, uses readeither
    . included task path support in:
        fill_cgroup_cvt, fill_cmdline_cvt,
        read_unvectored
    . QUICK_THREADS #define allows copying
      process info vs. repeatedly reading
    . simple_nexttid no longer values ppid
    . path var made non-static in readtask
    . documented 'proc_data_t' in .h file
    . tweaked some c comments & formatting
   library.map
    . added new readeither, readproctab3
 Program changes
   ps
    . exploits readproctab3 where possible
    . improved args/comm compliance
   top
    . exploits readeither