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

src/lib.rs

@@ -1,2 +1,8 @@
-generate::from_witx!();
-
+pub mod test {
+    generate::from_witx!("test.witx");
+}
+/*
+pub mod wasi {
+    generate::from_witx!("crates/WASI/phases/snapshot/witx/wasi_snapshot_preview1.witx");
+}
+*/