library: rename those readstat.c & h sources to 'stat'

In an attempt to normalize the 'stat' interface, we'll
first shed any reminders of the old readproc interface
by changing file names to be more descriptive & brief.

Signed-off-by: Jim Warner <james.warner@comcast.net>

proc/procps.h

@@ -23,8 +23,8 @@
 #include <proc/meminfo.h>
 #include <proc/namespace.h>
 #include <proc/pids.h>
-#include <proc/readstat.h>
 #include <proc/slab.h>
+#include <proc/stat.h>
 #include <proc/sysinfo.h>
 #include <proc/version.h>
 #include <proc/vmstat.h>