[MEDIUM] implement the CSV output for the statistics

It is now possible to get CSV ouput from the statistics by
simply appending ";csv" to the HTTP request sent to get the
stats. The fields keep the same ordering as in the HTML page,
and a field "pxname" has been prepended at the beginning of
the line.
diff --git a/include/proto/dumpstats.h b/include/proto/dumpstats.h
index 3fc14e7..cecfbe2 100644
--- a/include/proto/dumpstats.h
+++ b/include/proto/dumpstats.h
@@ -27,6 +27,8 @@
 #include <types/buffers.h>
 #include <types/session.h>
 
+#define STAT_FMT_HTML 0x1
+
 int stats_dump_http(struct session *s, struct uri_auth *uri, int flags);
 int stats_dump_proxy(struct session *s, struct proxy *px, struct uri_auth *uri, int flags);