ENH: Allow usecols to accept callable (GH14154)
- [ X] closes #14154 
- [ X] tests added / passed
- [ X] passes `git diff upstream/master | flake8 --diff`
- [X ] whatsnew entry
  <img width="1515" alt="asv_bench" src="https://cloud.githubusercontent.com/assets/609873/18575075/942a9240-7ba1-11e6-9dca-bab8b9987f31.png">
