sql: Add DATE/TIMESTAMP/INTERVAL parameters

[vivekmenezes]

These parameter types have to be embedded in the sql. Allow passing these as parameters.

[petermattis]

Supporting date/timestamp parameters should be straightforward (we're already passing time.Time parameters to the server, just not using them). Passing interval will be more interesting as there is not native support for time.Duration. While that type is simply an int64, I worry about the type checking after FillArgs is called. Argument filling might need to be augmented so that it is passed the expected type of the argument. Maybe. I haven't looked at this enough to be sure.

[vivekmenezes]

I think we can have the user specify the type in the SQL. So when passing in an interval they would use an int64 and specify "INTERVAL $3" in the sql. Same with Date, "Date $4," where $4 is of type time.Time

[petermattis]

Ah, yes, that should work.