Controller: trivial abilities to save and request configuration.

Now you can get current configuration with:

   $ curl 127.0.0.1:8443

and put new configuration with:

   $ curl -X PUT -d @conf.json 127.0.0.1:8443

src/nxt_conf.h

@@ -12,7 +12,7 @@
 typedef struct nxt_conf_json_value_s  nxt_conf_json_value_t;
 
 
-nxt_conf_json_value_t *nxt_conf_json_parse(nxt_buf_mem_t *b,
+nxt_conf_json_value_t *nxt_conf_json_parse(u_char *pos, size_t length,
     nxt_mem_pool_t *pool);
 nxt_buf_t *nxt_conf_json_print(nxt_conf_json_value_t *value,
     nxt_mem_pool_t *pool);