REORG: include: move common/memory.h to haproxy/pool.h

Now the file is ready to be stored into its final destination. A few
minor reorderings were performed to keep the file properly organized,
making the various sections more visible (cache & lockless).

In addition and to stay consistent, memory.c was renamed to pool.c.
diff --git a/include/proto/log.h b/include/proto/log.h
index ef792c8..48802dc 100644
--- a/include/proto/log.h
+++ b/include/proto/log.h
@@ -27,7 +27,7 @@
 #include <syslog.h>
 
 #include <haproxy/api.h>
-#include <common/memory.h>
+#include <haproxy/pool.h>
 #include <haproxy/thread-t.h>
 
 #include <types/log.h>