Dataframe-sql

This update includes all enhancements from the latest release of sql_to_ibis

* This update includes the latest changes to sql to ibis - tables with the same column names can now be joined

* This update includes the latest changes to sql to ibis - spaces are now permitted in column names, using double quotes

- sql_to_ibis has now been updated to version 0.3.0 and includes an update to ibis
- the updated ibis includes some set operations, like intersect and except that were previously not available
- Included in this release are some bug fixes relating to strings and null values, for all updates to the sql dialect (there are only additions nothing should be removed) see [sql_to_ibis](https://github.com/zbrookle/sql_to_ibis)

This update adds the readme documentation to the PyPi page.

Also, a note for anyone following development of this package. All SQL related changes and errors are actually a part of [sql_to_ibis](https://github.com/zbrookle/sql_to_ibis), so when watching for new releases in terms of SQL functionality, please refer to that repo

The backend will be switched to the package, sql_to_ibis, a different package that I wrote that interfaces with Ibis, a package using set expressions with various backends. This will remove a couple features that are currently present, which will be re added in the future when they are added to ibis's pandas backend, such as support for rank. However, overall the switch will make this package much more robust and reliable