reorganize database crate.

split database Cork into unit.

split database migrations from mod.rs

Signed-off-by: Jason Volk <jason@zemos.net>

src/database/cork.rs

@@ -0,0 +1,32 @@
+use std::sync::Arc;
+
+use super::KeyValueDatabaseEngine;
+
+pub struct Cork {
+	db: Arc<dyn KeyValueDatabaseEngine>,
+	flush: bool,
+	sync: bool,
+}
+
+impl Cork {
+	pub(crate) fn new(db: &Arc<dyn KeyValueDatabaseEngine>, flush: bool, sync: bool) -> Self {
+		db.cork().unwrap();
+		Cork {
+			db: db.clone(),
+			flush,
+			sync,
+		}
+	}
+}
+
+impl Drop for Cork {
+	fn drop(&mut self) {
+		self.db.uncork().ok();
+		if self.flush {
+			self.db.flush().ok();
+		}
+		if self.sync {
+			self.db.sync().ok();
+		}
+	}
+}