checkin initial MVCC codebase

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

mini-lsm-mvcc/src/lib.rs

@@ -0,0 +1,14 @@
+pub mod block;
+pub mod compact;
+pub mod debug;
+pub mod iterators;
+pub mod key;
+pub mod lsm_iterator;
+pub mod lsm_storage;
+pub mod manifest;
+pub mod mem_table;
+pub mod table;
+pub mod wal;
+
+#[cfg(test)]
+mod tests;