bump to 0.15.2

bump to 0.15.1

create 0.15 branch

fix cast() with mysql (juicedata#590)

* fix cast() with mysql

* ignore the error from read-only database

bump to 0.14.2

bump to 0.14.1

bump to 0.13.1

bump to 0.13.0

bump to 0.12.1

bump to 0.12