slurp! mechanism

You might find my slurp! method handy - see README.md for example of how it will automatically slurp a spreadsheet by using the sheet names to find the model class. If it can't find it then it will warn and move on to the next.

I added a couple of options that should be non-invasive to import! ... :delete and :sheet. You may want to have import! look for a sheet name based on the model class or table name ... or just leave with selecting the first sheet of the workbook.

Thanks!