While it's perfectly OK for software to start enumerating from 0, human calendar tradition starts calendaring at 1. I suspect that in the future (if not already) there could be small confusion with humans referring to week N of year Y when in fact current version refers to week N-1 of year Y. 

Example: /timeline?yw=2013-00&n=2000 shows week 0 of year 2013, which for a human corresponds to the first week of year 2013.

If it does not break current codebase, my suggestion is that this is resolved in favor of usual human interpretation (i.e. first week of the year is numeral 1, not 0).

/reports?view=byweek should show week numbers starting at 1