feat: change dummy c to a rust plugin example

examples/custom_plugin/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "custom_plugin"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[lib]
+name = "custom_plugin"
+path = "src/lib.rs"
+crate-type = ["cdylib"]
+
+[dependencies]
+lazy_static = "1.4.0"
+rustdesk = { path = "../../", version = "1.2.0"}
+
+[profile.release]
+lto = true
+codegen-units = 1
+panic = 'abort'
+strip = true
+#opt-level = 'z' # only have smaller size after strip
+rpath = true