MAJOR: chunks: replace struct chunk with struct buffer

Now all the code used to manipulate chunks uses a struct buffer instead.
The functions are still called "chunk*", and some of them will progressively
move to the generic buffer handling code as they are cleaned up.
diff --git a/src/hpack-dec.c b/src/hpack-dec.c
index 7c4147b..16a722f 100644
--- a/src/hpack-dec.c
+++ b/src/hpack-dec.c
@@ -114,7 +114,8 @@
  * allocated there. In case of allocation failure, returns a string whose
  * pointer is NULL.
  */
-static inline struct ist hpack_alloc_string(struct chunk *store, int idx, struct ist in)
+static inline struct ist hpack_alloc_string(struct buffer *store, int idx,
+					    struct ist in)
 {
 	struct ist out;
 
@@ -148,7 +149,8 @@
  * can use list[].n.len == 0 as a marker for the end of list.
  */
 int hpack_decode_frame(struct hpack_dht *dht, const uint8_t *raw, uint32_t len,
-                       struct http_hdr *list, int list_size, struct chunk *tmp)
+                       struct http_hdr *list, int list_size,
+                       struct buffer *tmp)
 {
 	uint32_t idx;
 	uint32_t nlen;