Expose transaction::TransactionProgress as public (#401)

* Update transaction.rs

* documentation

* Update src/transaction.rs

Co-authored-by: James Wilson <james@jsdw.me>

* fmt

Co-authored-by: James Wilson <james@jsdw.me>

src/transaction.rs

@@ -57,7 +57,8 @@ pub struct TransactionProgress<'client, T: Config> {
 impl<'client, T: Config> Unpin for TransactionProgress<'client, T> {}
 
 impl<'client, T: Config> TransactionProgress<'client, T> {
-    pub(crate) fn new(
+    /// Instantiate a new [`TransactionProgress`] from a custom subscription.
+    pub fn new(
         sub: RpcSubscription<SubstrateTransactionStatus<T::Hash, T::Hash>>,
         client: &'client Client<T>,
         ext_hash: T::Hash,