Generate shell completions with clap during build (#327)

* Generate shell completions with clap during build

* Updated ci release script, added SHELL_COMPLETIONS_DIR override to build.rs and fixed dependency version

build.rs

@@ -0,0 +1,26 @@
+#[macro_use]
+extern crate clap;
+
+use clap::Shell;
+use std::fs;
+
+include!("src/clap_app.rs");
+
+const BIN_NAME: &str = "bat";
+
+fn main() {
+    let outdir = std::env::var_os("SHELL_COMPLETIONS_DIR").or(std::env::var_os("OUT_DIR"));
+
+    let outdir = match outdir {
+        None => return,
+        Some(outdir) => outdir,
+    };
+
+    fs::create_dir_all(&outdir).unwrap();
+
+    let mut app = build_app(true);
+    app.gen_completions(BIN_NAME, Shell::Bash, &outdir);
+    app.gen_completions(BIN_NAME, Shell::Fish, &outdir);
+    app.gen_completions(BIN_NAME, Shell::Zsh, &outdir);
+    app.gen_completions(BIN_NAME, Shell::PowerShell, &outdir);
+}