Add ADO Support

[theory]

Add URI::_ado with the ability to return a DBD::ADO DSN from dbi_dsn(). Need to ascertain what are the best parameters to use, since default params seem to be dependent on the Provider parameter value. What should its value be, if it is not in the query string part of the URI?

[theory]

Added simple URI::_ado in 51cc3ab, along with the ability to pass a driver name to URI::mssql's dbi_dsn() method to get an alternate DSN. Pass "ado" to get back a DBD::ADO DSN.

At this point, it includes no default Provider value, and simply adds all the same parameters as URI::_odbc does. Feedback on what parameters to use by default would be greatly appreciated. It might even make sense to use different default parameters if the Provider value is in the query portion of the URI, yes? Recommendations and pull requests wanted!