Add support for .xbm bitmap file

.xbm is easy to include in C as source file. It could be viewed
and edited directly without need to be converted between images
and C array.

src/resource.c

@@ -0,0 +1,18 @@
+#include "resource.h"
+
+#include "res/bluetooth.xbm"
+#include "res/foss-asia-2.xbm"
+
+xbm_t bluetooth = {
+	.bits = bluetooth_bits, 
+	.w = bluetooth_width, 
+	.h = bluetooth_height,
+	.fh = 11
+};
+
+xbm_t splash = {
+	.bits = foss_asia_2_bits, 
+	.w = foss_asia_2_width, 
+	.h = foss_asia_2_height,
+	.fh = 11
+};