Vendor dependencies for 0.3.0 release

vendor/variadics_please/documentation/debugging.md

@@ -0,0 +1,8 @@
+# Debugging
+
+## Macro Debugging
+
+- Print the final output of a macro using `cargo rustc --profile=check -- -Zunstable-options --pretty=expanded`
+  - Alternatively you could install and use [cargo expand](https://github.com/dtolnay/cargo-expand) which adds syntax highlighting to the terminal output.
+    - Additionally get pager by piping to `less` ( on Unix systems ): `cargo expand --color always | less -R`
+- Print output during macro compilation using `eprintln!("hi");`