Provide member summary for previous months

Hi,

This is in regard to a message I posted on the developers' forum on Jan. 29, in which I asked about displaying membership information summaries for selected periods rather than just the current time. I've implemented that functionality and attached it. The upshot is that you can now issue a query containing "date=yyyymm" and get a year-to-date summary for the specified period. If the date happens to be the current year/month, or if it's missing, you get the same display as before.

The change spans 3 files. I added some new functions, and added optional arguments to others. In general I tried to ensure that any existing code would be unaffected.