Handle multiple parameters with CommaSeparated attribute

[derekpuff]

Thank you for this excellent approach to handling the query string. I found that it does not correctly handle a query string with multiple parameters that have comma-separated values.

GET /products?sizes=s,m,l&colors=blue,green

[HttpGet("Products")] public IActionResult Get( [CommaSeparated]IEnumerable<string> sizes, [CommaSeparated]IEnumerable<string> colors, string filterText)

Presumably the fix involves having the various classes (the factory and provider) maintain an enumeration of keys. Thanks!

[chriscab83]

I just created a pull request for the handling of multiple comma-separated values.