Add an env var to change the fuzzy finder

src/config.rs

@@ -68,3 +68,10 @@ pub fn zo_resolve_symlinks() -> bool {
         None => false,
     }
 }
+
+pub fn zo_fuzzy_finder_cmd() -> &'static str {
+    match env::var_os("_ZO_FUZZY_FINDER_CMD") {
+        Some(sk) if sk == "skim" => "skim",
+        _ => "fzf",
+    }
+}