library: cleanup of library includes

The includes used to define a lot of things a library include
should not. It was also a bit messy what was exposed in the library
and what was not.

get_pid_digits -> procps_pid_length and exported correctly

MALLOC attribute move into relevant .c files
NORETURN attribute moved to relevant .c, not used in library
PURE attribute removed, it wasn't used
KLONG/KLF/STRTOUKL were fixed for long, so now just use long

HIDDEN attribute removed. It was for 3 functions. The PROCPS_EXPORT
seems to do the same (opposite) thing.

likely/unlikely removed from most places, its highly debateable
this does anything useful as CPUs have gotten smarter about branches.

Re-arranged the includes, ALL external programs should just #include
<proc/procps.h> then proc/procps.h includes headers for files that
have exported functions. procps.h and the headers it includes should
not use items that are not exportable (e.g. hidden functions or
macros) they go in procps-private.h

proc/wchan.h

@@ -1,7 +1,7 @@
 #ifndef PROCPS_PROC_WCHAN_H
 #define PROCPS_PROC_WCHAN_H
 
-#include <proc/procps.h>
+#include <features.h>
 
 __BEGIN_DECLS