Update sql.py to distinguish between BigInt, Integer, and SmallInt
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This is to resolve #37344.  I've never contributed to Pandas before, so may need guidance to proceed.
Hello @pilotjoe! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-10-29 15:01:03 UTC > Thanks @pilotjoe for the PR!
> 
> Can you add tests? That's the first thing we look at when reviewing. They would go into pandas/tests/io/test_sql.py

@arw2019 Thanks for pointing me to the tests.  I've incorporated tests for int64, int32, and int16. This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. this looks ok, but is stale. pls ping if you want to continue working.