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/common/hpack-tbl.h b/include/common/hpack-tbl.h
index 1d2a8bd..07e0a9f 100644
--- a/include/common/hpack-tbl.h
+++ b/include/common/hpack-tbl.h
@@ -31,7 +31,7 @@
 #include <haproxy/api.h>
 #include <common/http-hdr.h>
 #include <import/ist.h>
-#include <common/memory.h>
+#include <haproxy/pool.h>
 
 /* Dynamic Headers Table, usable for tables up to 4GB long and values of 64kB-1.
  * The model can be improved by using offsets relative to the table entry's end