SQL: move df.to_sql to generic + update with new functionality
Initial commit for this.

Questions:
- To catch Panels (and raiseNotImplementedError), should I do this in sql.to_sql or in NDFrame.to_sql?
- To support Series, I can just call `to_frame` on it. Is this OK?

And should add tests for this.

I would to this in `sql.to_sql` (then `NDFrame.to_sql` is pretty generic)

you can call `to_frame` on Series, sure
 added tests
