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/src/stick_table.c b/src/stick_table.c
index 0fb0927..bd7f97f 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -16,7 +16,7 @@
 
 #include <haproxy/api.h>
 #include <common/cfgparse.h>
-#include <common/memory.h>
+#include <haproxy/pool.h>
 #include <haproxy/list.h>
 #include <common/net_helper.h>
 #include <common/standard.h>