import some other helpers from pat's crate

* parse the proc macro argument into a file path
* use a much simpler witx spec by default

crates/generate/src/lib.rs

@@ -1,10 +1,16 @@
 extern crate proc_macro;
 
 mod imp;
+mod parse;
 
 use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
 
 #[proc_macro]
-pub fn from_witx(_args: TokenStream) -> TokenStream {
-    TokenStream::from(imp::gen())
+pub fn from_witx(args: TokenStream) -> TokenStream {
+    let args = TokenStream2::from(args);
+    let witx_paths = parse::witx_paths(args).expect("parsing macro arguments");
+    let doc = witx::load(&witx_paths).expect("loading witx");
+    let out = imp::gen(doc);
+    TokenStream::from(out)
 }