rocksdb 5.5.1 release post

Summary:
https://github.com/facebook/rocksdb/releases/tag/v5.5.1
Closes https://github.com/facebook/rocksdb/pull/2522

Differential Revision: D5365355

Pulled By: lightmark

fbshipit-source-id: 63371a98ebc7429766fd86dc27c1ea35950c98f5

docs/_data/authors.yml

@@ -56,3 +56,7 @@ ajkr:
 sagar0:
   full_name: Sagar Vemuri
   fbid: 2419111
+
+lightmark:
+  full_name: Aaron Gao
+  fbid: 1351549072

docs/_posts/2017-06-29-rocksdb-5-5-1-released.markdown

@@ -0,0 +1,22 @@
+---
+title: RocksDB 5.5.1 Released!
+layout: post
+author: lightmark
+category: blog
+---
+
+### New Features
+* FIFO compaction to support Intra L0 compaction too with CompactionOptionsFIFO.allow_compaction=true.
+* Statistics::Reset() to reset user stats.
+* ldb add option --try_load_options, which will open DB with its own option file.
+* Introduce WriteBatch::PopSavePoint to pop the most recent save point explicitly.
+* Support dynamically change `max_open_files` option via SetDBOptions()
+* Added DB::CreateColumnFamilie() and DB::DropColumnFamilies() to bulk create/drop column families.
+* Add debugging function `GetAllKeyVersions` to see internal versions of a range of keys.
+* Support file ingestion with universal compaction style
+* Support file ingestion behind with option `allow_ingest_behind`
+* New option enable_pipelined_write which may improve write throughput in case writing from multiple threads and WAL enabled.
+
+### Bug Fixes
+* Fix the bug that Direct I/O uses direct reads for non-SST file
+* Fix the bug that flush doesn't respond to fsync result