Add another crate for a proc macro

Cargo.lock

@@ -5,3 +5,7 @@ version = 3
 [[package]]
 name = "nih-plug"
 version = "0.1.0"
+
+[[package]]
+name = "nih-plug-derive"
+version = "0.1.0"

Cargo.toml

@@ -1,2 +1,2 @@
 [workspace]
-members = ["nih-plug"]
+members = ["nih-plug", "nih-plug-derive"]

nih-plug-derive/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "nih-plug-derive"
+version = "0.1.0"
+edition = "2021"
+authors = ["Robbert van der Helm <mail@robbertvanderhelm.nl>"]
+license = "GPL-3.0-or-later"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = "1.0"
+quote = "1.0"

nih-plug-derive/src/lib.rs

@@ -0,0 +1,8 @@
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        let result = 2 + 2;
+        assert_eq!(result, 4);
+    }
+}