spice: make compression configurable.

This patch adds options to the -spice command line switch to
configure image compression.

[ v2: speling fix in the documentation ]
diff --git a/qemu-config.c b/qemu-config.c
index 26748a5..8b545b1 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -391,6 +391,15 @@
         },{
             .name = "tls-ciphers",
             .type = QEMU_OPT_STRING,
+        },{
+            .name = "image-compression",
+            .type = QEMU_OPT_STRING,
+        },{
+            .name = "jpeg-wan-compression",
+            .type = QEMU_OPT_STRING,
+        },{
+            .name = "zlib-glz-wan-compression",
+            .type = QEMU_OPT_STRING,
         },
         { /* end if list */ }
     },