Move crates under a sub folder to clean up the code

crates/flatten-serde-json/src/main.rs

@@ -0,0 +1,11 @@
+use std::io::stdin;
+
+use flatten_serde_json::flatten;
+use serde_json::{Map, Value};
+
+fn main() {
+    let json: Map<String, Value> = serde_json::from_reader(stdin()).unwrap();
+
+    let result = flatten(&json);
+    println!("{}", serde_json::to_string_pretty(&result).unwrap());
+}