Include CSS as GResource

Also use explicit namespace for bare functions and constants used in
main.rs.

build.rs

@@ -0,0 +1,7 @@
+use glib_build_tools::compile_resources;
+
+
+
+fn main() {
+  compile_resources(&["data"], "data/zoodex.gresource.xml", "zoodex.gresource");
+}