Better file naming of generated reports

This is a great little module... but once a user starts downloading multiple reports, it would be easier to quickly distinguish reports from one another if each report was named with the title, instead of "customreports-10-02-10.csv".

Additionally, I would like to recommend a date pattern other than "d-m-y", which is usually very confusing (as seen in my example above). "Y-m-d" would produce "2010-02-10".

Attached is a patch which accomplishes these two improvements.