Update command timeout (and all time-based parameters) to TimeSpan

[casperOne]

I suspect this should be grouped under #688 since this is a breaking change.

I've always hated how commandTimeout was typed as an int; .NET has always had an abstraction for time in the TimeSpan structure.

Exposing commandTimeout as a TimeSpan from Dapper would prevent the need for creating convenience wrappers and make readability/usability much better IMO.

Anecdotally, I have to look up the syntax every time I need to use commandTimeout as I can't remember if it's seconds or milliseconds.