ENH: Named aggregations with multiple columns
- [ ] closes #29268
- [x] tests added
  - [ ] tests passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @fpunny! 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 2020-04-08 02:24:07 UTC Thanks @fpunny for the PR. can you please add tests and a whatsnew and update docstrings/examples etc so users would know how to use this functionality. @simonjayhawkins Hi simon, we created the whatsnew entry, added some test cases, and passed all of the checks. This being our first enhancement for Pandas, we're hoping to get some feedback on our implementation. We're fairly new to the codebase, hence we would love to learn a bit more about how we can improve - in hopes of merging this This MR seems inactive, how complex is this issue to pick up as a first issue? @jreback  this particular issue is a bit complex

however my comments above about simplifying the existing code could be a good first issue Closing as I think this has gone stale, but @fpunny ping if you'd like to pick back up @WillAyd If OP does not have time, I can give this a try, not sure if I can make it, but I would like to see how far I come.  Sounds good! Feel free to clone this and push a new PR