Update HISTORY.md
Update HISTORY.md

Summary:
Move some of the items in public API changes section to to new
features section.

Test Plan: no code change.

Reviewers: igor, sdong, anthony, IslamAbdelRahman

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D50229

norton/rocksdb,Andymic/rocksdb,bbiao/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,hobinyoon/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,Vaisman/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,Andymic/rocksdb,facebook/rocksdb,wenduo/rocksdb,norton/rocksdb,ryneli/rocksdb,facebook/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,OverlordQ/rocksdb,vmx/rocksdb,bbiao/rocksdb,vmx/rocksdb,OverlordQ/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,flabby/rocksdb,facebook/rocksdb,bbiao/rocksdb,hobinyoon/rocksdb,wenduo/rocksdb,flabby/rocksdb,norton/rocksdb,tsheasha/rocksdb,flabby/rocksdb,jalexanderqed/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,vmx/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb,flabby/rocksdb,facebook/rocksdb,SunguckLee/RocksDB,OverlordQ/rocksdb,Andymic/rocksdb,Andymic/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,ryneli/rocksdb,facebook/rocksdb,ryneli/rocksdb,Vaisman/rocksdb,Vaisman/rocksdb,tsheasha/rocksdb,norton/rocksdb,facebook/rocksdb,Andymic/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,ryneli/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,Vaisman/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,vmx/rocksdb,bbiao/rocksdb,jalexanderqed/rocksdb,norton/rocksdb,flabby/rocksdb,flabby/rocksdb,jalexanderqed/rocksdb,bbiao/rocksdb,norton/rocksdb,wenduo/rocksdb,Vaisman/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,Vaisman/rocksdb,OverlordQ/rocksdb,wenduo/rocksdb,vmx/rocksdb,facebook/rocksdb,norton/rocksdb,SunguckLee/RocksDB,wenduo/rocksdb,ryneli/rocksdb,norton/rocksdb,Andymic/rocksdb,flabby/rocksdb,Vaisman/rocksdb,ryneli/rocksdb,wenduo/rocksdb,wat-ze-hex/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,ryneli/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,facebook/rocksdb,tsheasha/rocksdb,jalexanderqed/rocksdb