Support valid *non-alphanumeric* characters in table name

From the [documentation](http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Limits.html)
> Table names and secondary index names
> For table and secondary index names, allowed characters are a-z, A-Z, 0-9, '_' (underscore), '-' (dash), and '.' (dot). Names can be between 3 and 255 characters long.