* move database settings from models to setting

* update docs

* fix checkout pr

* fix tests

* fix lint

* remove unsupported tidb options

* correct wrong variable name

* remove tidb totally

This adds a sqlite build tag so that you don't have to have the sqlite
import commented out in code and users can run:
    go build -tags sqlite
if they want to have sqlite support enabled.  It is disabled by default
so nothing changes with the default go get or build commands.