Reorganise build script into modules

build/main.rs

@@ -0,0 +1,10 @@
+#[cfg(feature = "application")]
+mod application;
+mod util;
+
+fn main() -> anyhow::Result<()> {
+    #[cfg(feature = "application")]
+    application::gen_man_and_comp()?;
+
+    Ok(())
+}