display the git revision version information (#105)

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/solidity/build.rs

@@ -0,0 +1,9 @@
+fn main() {
+    let git_rev = std::process::Command::new("git")
+        .args(["rev-parse", "--short", "HEAD"])
+        .output()
+        .map(|out| String::from_utf8(out.stdout).unwrap_or_default())
+        .unwrap_or("unknown".to_owned());
+
+    println!("cargo:rustc-env=GIT_COMMIT_HASH={}", git_rev.trim());
+}