db+adapter, add sqlx + schema & add adapter

Adds SQLX for database management, and an Adapter interface for
interacting with it. Through the type "AdapterPool"

Creates an initial_schema with everything I think I'll need.

koucha/src/lib.rs

@@ -3,3 +3,36 @@ use std::error::Error;
 type Result<T> = std::result::Result<T, Box<dyn Error>>;
 
 pub mod score;
+pub struct AdapterPool(sqlx::SqlitePool);
+pub struct AdapterBuilder {
+  database_url: String,
+}
+
+impl AdapterBuilder {
+  pub fn new() -> Self {
+    Self {
+      database_url: "sqlite:test.db".to_string(),
+    }
+  }
+
+  pub fn database_url(mut self, url: &str) -> Self {
+    self.database_url = url.to_string();
+    self
+  }
+
+  pub async fn create(self) -> Result<Adapter> {
+    let db = sqlx::sqlite::SqlitePoolOptions::new()
+      .connect(&self.database_url).await?;
+    sqlx::migrate!().run(&db).await?;
+
+    Ok(Adapter { db: AdapterPool(db) })
+  }
+}
+
+pub struct Adapter {
+  db: AdapterPool,
+}
+
+impl Adapter {
+  pub fn get_pool(&self) -> &AdapterPool { &self.db }
+}