Add bash completion

Closes https://github.com/sharkdp/bat/issues/1010

build.rs

@@ -54,6 +54,11 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         "assets/manual/bat.1.in",
         out_dir.join("assets/manual/bat.1"),
     )?;
+    template(
+        &variables,
+        "assets/completions/bat.bash.in",
+        out_dir.join("assets/completions/bat.bash"),
+    )?;
     template(
         &variables,
         "assets/completions/bat.fish.in",