MINOR: acl: add a function to dump the list of known ACL keywords

New function acl_dump_kwd() dumps the registered ACL keywords and their
sample-fetch equivalent to stdout. It's called by dump_registered_keywords()
for keyword class "acl".
diff --git a/src/haproxy.c b/src/haproxy.c
index 16fafc3..72c065e 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -1825,6 +1825,7 @@
 		if (strcmp(kwd_dump, "help") == 0) {
 			printf("# List of supported keyword classes:\n");
 			printf("all: list all keywords\n");
+			printf("acl: ACL keywords\n");
 			printf("cfg: configuration keywords\n");
 			printf("cli: CLI keywords\n");
 			printf("flt: filter names\n");
@@ -1835,6 +1836,11 @@
 			all = 1;
 		}
 
+		if (all || strcmp(kwd_dump, "acl") == 0) {
+			printf("# List of registered ACL keywords:\n");
+			acl_dump_kwd();
+		}
+
 		if (all || strcmp(kwd_dump, "cfg") == 0) {
 			printf("# List of registered configuration keywords:\n");
 			cfg_dump_registered_keywords();