add wal and manifest

Signed-off-by: Alex Chi Z <iskyzh@gmail.com>

mini-lsm/src/wal.rs

@@ -0,0 +1,19 @@
+use std::path::Path;
+
+use anyhow::Result;
+
+pub struct Wal {}
+
+impl Wal {
+    pub fn create(path: impl AsRef<Path>) -> Result<Self> {
+        unimplemented!()
+    }
+
+    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
+        Ok(())
+    }
+
+    pub fn sync(&self) -> Result<()> {
+        Ok(())
+    }
+}