*: bump to v2.1.15 (tikv#1644)

Signed-off-by: youjiali1995 <zlwgx1023@gmail.com>

Bump version to 3.0.1 (tikv#1640)

Signed-off-by: Shafreeck Sea <shafreeck@gmail.com>

changelog: add v2.1.14 changelog (tikv#1618)

Signed-off-by: disksing <i@disksing.com>

Version 3.0.0

bump to v3.0.0-rc.3 (tikv#1592)

Signed-off-by: Connor1996 <zbk602423539@gmail.com>

update CHANGELOG for 2.1.12 (tikv#1579)

Signed-off-by: qupeng <qupeng@pingcap.com>

update CHANGELOG for 2.1.12 (tikv#1579)

Signed-off-by: qupeng <qupeng@pingcap.com>

pick some hot region optimization to release 2.1 (tikv#1551)

*: make hot region scheduler configurable (tikv#1412)

Signed-off-by: nolouch <nolouch@gmail.com>

* use high priority for the hot region related operators (tikv#1492)

Signed-off-by: Ryan Leung <rleungx@gmail.com>

* schedulers: let hot region balance not affect by balance-region-scheduler-limit (tikv#1522)

Signed-off-by: nolouch <nolouch@gmail.com>