REORG: memory: move the pool type definitions to haproxy/pool-t.h

This is the beginning of the move and cleanup of memory.h. This first
step only extracts type definitions and basic macros that are needed
by the files which reference a pool. They're moved to pool-t.h (since
"pool" is more obvious than "memory" when looking for pool-related
stuff). 3 files which didn't need to include the whole memory.h were
updated.
diff --git a/include/types/capture.h b/include/types/capture.h
index 493d0be..7849cdd 100644
--- a/include/types/capture.h
+++ b/include/types/capture.h
@@ -23,7 +23,7 @@
 #define _TYPES_CAPTURE_H
 
 #include <haproxy/api-t.h>
-#include <common/memory.h>
+#include <haproxy/pool-t.h>
 
 struct cap_hdr {
     struct cap_hdr *next;