Require Western Arabic (ASCII) numerals for max_rows

Hi Jim,

Previously, any Unicode character with the `General_Category` property of `Decimal_Number` was permitted as the value of `max_rows`.  This included Eastern Arabic numerals like `٤٠` and Devanagari numerals like `४०` (both represent the Western Arabic `40`).  However, `max_rows` was later being used with the numeric equality operator `==`, which only understands Western Arabic numerals.  I fixed this by replacing `\d` in the validation regex with `[0-9]` so that only `0` through `9` are valid and no other of the `Decimal_Number` characters.  Two tests were also added.

Best,
Nick