Start work on parsing of graphics escape code

kitty/graphics.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (C) 2017 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#pragma once
+
+typedef struct {
+    unsigned char action, transmission_type;
+    uint32_t format, more, id;
+    uint32_t width, height, x_offset, y_offset, data_height, data_width, num_cells, num_lines;
+    int32_t z_index;
+    char payload[4096];
+} GraphicsCommand;