MINOR: compression: memlevel and windowsize

The window size and the memlevel of the zlib are now configurable using
global options tune.zlib.memlevel and tune.zlib.windowsize.

It affects the memory consumption of the zlib.
diff --git a/src/haproxy.c b/src/haproxy.c
index c6933c3..d85a46a 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -126,6 +126,12 @@
 #ifdef USE_OPENSSL
 		.sslcachesize = 20000,
 #endif
+#ifdef USE_ZLIB
+		.zlibmemlevel = 8,
+		.zlibwindowsize = MAX_WBITS,
+#endif
+
+
 	},
 #ifdef USE_OPENSSL
 #ifdef DEFAULT_MAXSSLCONN