Implement timeSlice function

[grzkv]

There is currently no timeSlice function in this implementation of graphite as defined here. It would be nice to have it.

[paskal]

I've tried for two days, and either I am missing something very basic, or project data model really doesn't allow proper date parsing within graphite functions (app.defaultTimeZone is unreachable outside of app instance). Whoever had to implement only other function with types.Date parsing (linearRegression) seems to be stunned by the same error: date arguments parsing is not implemented for it at all.
date.DateParamToEpoch seems to be the way to parse types.Date but there is no way to consider app-wise configuration within graphite function call without rewriting bug chunk of the program: python graphite read global settings to parse the time.
I think someone more familiar with the project and with stronger opinion on this matter should implement this in a desired way.

[grzkv]

I agree that the code organization on that part is not perfect. Also, I think the #200 by @KozzyKoder is related.

On top of that, there are currently some problems with timezones in carbonapi the issue is not fully understood IMO, so I did not file it here yet.