MINOR: cache: report the number of cache lookups and cache hits

The cache lookups and hits is now accounted per frontend and per backend,
and reported on the stats page.
diff --git a/include/types/counters.h b/include/types/counters.h
index 79dd6d4..1898548 100644
--- a/include/types/counters.h
+++ b/include/types/counters.h
@@ -56,6 +56,8 @@
 			long long comp_rsp;     /* number of compressed responses */
 			unsigned int rps_max;   /* maximum of new HTTP requests second observed */
 			long long rsp[6];       /* http response codes */
+			long long cache_lookups;/* cache lookups */
+			long long cache_hits;   /* cache hits */
 		} http;
 	} p;                                    /* protocol-specific stats */
 };
@@ -105,6 +107,8 @@
 			long long comp_rsp;     /* number of compressed responses */
 			unsigned int rps_max;   /* maximum of new HTTP requests second observed */
 			long long rsp[6];       /* http response codes */
+			long long cache_lookups;/* cache lookups */
+			long long cache_hits;   /* cache hits */
 		} http;
 	} p;                                    /* protocol-specific stats */
 };