db, add core user functionality and tests; db mod

Adds all the basic user functions, and tests for them.

This is also intializes the DB Module, which will have more things in it

koucha/src/lib.rs

@@ -2,6 +2,7 @@ use std::error::Error;
 
 type Result<T> = std::result::Result<T, Box<dyn Error>>;
 
+pub mod db;
 pub mod score;
 
 #[cfg(test)]