Better handling of from and until parameters:
 - parsing Graphite date formats (HH:MM_YYYYMMDD, YYYYMMDD, MM/DD/YY)
 - if not specified, until defaults to now
 - if not specified, from defaults to now - 24 hours
Merge pull request #3 from oriordan/datesupport

adding support for multiple Graphite date formats for from and until