Convenience: Allow start/end to be given as year-integers

[zauster]

Hey,

i use always annual data (and it's also the default value). So it would be convenient to let the user specify only start = 2005 or end = 2005 if freq = "annual". start = 2005 would expand to 2005-01-01 and end = 2005 to 2005-12-31.
What do you think of that?

[ChrisMuir]

I like this idea, thanks for the suggestion! I may have some time this week to do this, otherwise this weekend.

Thanks again!

[ChrisMuir]

Just pushed this feature.

Now, when arg freq is set to "annual", these inputs for both start_date and end_date would all be valid: "2016-01-01", "2016", and 2016.

When arg freq is set to "monthly", these inputs for bot start_date and end_date would all be valid: "2016-01-01" and "2016-01".

Thanks again for suggesting this feature @zauster!