* feat(authorization): add authorization api
* feat(authorization): add check function
* feat(authorization): use hocon config file
* feat(authz): add mysql connector
* feat(authz): support pgsql
* feat(connector): support redis
* chore(authz): use "publish/subscribe/all" instead of "pub/sub/pubsub"
And move emqx app back to root level
After realising the challenges of developing plugins in standalone
rebar projects. it is perhaps more smooth to keep using emqx as
a rebar dependency
