Users expect Consolidated Sort to work with numeric values

[mcoles]

This is probably related to my confusion on #132.

Users often get confused about the fact that the Consolidated Sort field is actually sorting alphabetically, and then get unexpected results: https://community.tableau.com/thread/289915

This isn't helped by the fact that our demo uses numbers for the sort order.

Users can work around this problem by ensuring that their numbers are being treated as text, and ensuring that 0's are prepended to lower values that should precede later ones with more digits.

My proposal is that we do two things:

1. Improve the docs and demo in the short term to help avoid confusion.
2. Implement some "smarter" sorting in the longer term, such as is described in this post: https://ux.stackexchange.com/questions/95431/how-should-sorting-work-when-numeric-is-mixed-with-alpha-numeric