Add invite creation, removal, fetch and usage.

src/util/mod.rs

@@ -1,6 +1,14 @@
 use hashbrown::HashSet;
+use rand::{distributions::Alphanumeric, Rng};
 use std::iter::FromIterator;
 
 pub fn vec_to_set<T: Clone + Eq + std::hash::Hash>(data: &[T]) -> HashSet<T> {
     HashSet::from_iter(data.iter().cloned())
 }
+
+pub fn gen_token(l: usize) -> String {
+    rand::thread_rng()
+        .sample_iter(&Alphanumeric)
+        .take(l)
+        .collect::<String>()
+}