Add a separate client binary, with some common code to the server.

The cargo workspace thing was a PITA to figure out, but it seems to be working.  Could maybe be simplified?

Cargo.toml

@@ -3,7 +3,24 @@ name = "saslauthd"
 version = "0.2.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[workspace]
+members = [
+    "common",
+    "server",
+    "client",
+]
+
+#[workspace.dependencies]
+#clap = { version = "4.5.20", features = ["derive"] }
 
 [dependencies]
-structopt = "^0.3.26"
+clap = { version = "4.5.20", features = ["derive"] }
+common = { path = "common" }
+
+[[bin]]
+name = "saslauthd"
+path = "server/src/main.rs"
+
+[[bin]]
+name = "saslauthd_test_client"
+path = "client/src/main.rs"