Blog post for 5.1.2 release

Summary: Closes https://github.com/facebook/rocksdb/pull/1849

Differential Revision: D4528696

Pulled By: maysamyabandeh

fbshipit-source-id: c12f3a2

docs/_posts/2017-02-07-rocksdb-5-1-2-released.markdown

@@ -0,0 +1,15 @@
+---
+title: RocksDB 5.1.2 Released!
+layout: post
+author: maysamyabandeh
+category: blog
+---
+
+### Public API Change
+* Support dynamically change `delete_obsolete_files_period_micros` option via SetDBOptions().
+* Added EventListener::OnExternalFileIngested which will be called when IngestExternalFile() add a file successfully.
+* BackupEngine::Open and BackupEngineReadOnly::Open now always return error statuses matching those of the backup Env.
+
+### Bug Fixes
+* Fix the bug that if 2PC is enabled, checkpoints may loss some recent transactions.
+* When file copying is needed when creating checkpoints or bulk loading files, fsync the file after the file copying.