add version command

build.rs

@@ -0,0 +1,15 @@
+use std::process::Command;
+
+fn main() {
+    // get
+    let output = Command::new("git").args(&["rev-parse", "--short", "HEAD"]).output()
+        .expect("git rev-parse HEAD failed");
+    let hash = String::from_utf8(output.stdout).expect("not UTF-8 output");
+
+    let output = Command::new("git").args(&["rev-parse", "--abbrev-ref", "HEAD"]).output()
+        .expect("git rev-parse HEAD failed");
+    let branch = String::from_utf8(output.stdout).expect("not UTF-8 output");
+
+    println!("cargo:rustc-env=GIT_HASH={}", hash);
+    println!("cargo:rustc-env=GIT_BRANCH={}", branch);
+}