rename tools -> ra_tools

This should help with caching on CI I hope (see .travis.yml
before_cache)

crates/ra_tools/src/bin/pre-commit.rs

@@ -0,0 +1,28 @@
+use std::process::Command;
+
+use failure::bail;
+
+use ra_tools::{Result, run_rustfmt, run, project_root, Overwrite};
+
+fn main() -> Result<()> {
+    run_rustfmt(Overwrite)?;
+    update_staged()
+}
+
+fn update_staged() -> Result<()> {
+    let root = project_root();
+    let output = Command::new("git")
+        .arg("diff")
+        .arg("--diff-filter=MAR")
+        .arg("--name-only")
+        .arg("--cached")
+        .current_dir(&root)
+        .output()?;
+    if !output.status.success() {
+        bail!("`git diff --diff-filter=MAR --name-only --cached` exited with {}", output.status);
+    }
+    for line in String::from_utf8(output.stdout)?.lines() {
+        run(&format!("git update-index --add {}", root.join(line).to_string_lossy()), ".")?;
+    }
+    Ok(())
+}