Update HISTORY.md to include TimeOut write API and compaction update.

Summary: Update HISTORY.md to include TimeOut write API and compaction update.

Test Plan: n/a

Reviewers: ljin, sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19449
Finer report I/O stats about Flush and Compaction.

Summary:
This diff allows the I/O stats about Flush and Compaction to be reported
in a more accurate way.  Instead of measuring the size of a file, it
measure I/O cost in per read / write basis.

Test Plan: make all check

Reviewers: sdong, igor, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19383