Add a method to return the count by period with interval

[jeremyFreeAgent]

See #11 for the start of the talk.

[stephpy]

I'm +1 on @shouze comment:

bitDatePeriod needs to be renamed into bitDateRange as it looks confusing ATM A new method needs to be introduced, something like countByPeriodWithInterval(\DateTime $from, \DateTime $to, \DateInterval $interval). This method should return an array or any iterable object collection.

[stephpy]

On second point. Why does not use

countByPeriod(\DatePeriod $datePeriod) ?

[jeremyFreeAgent]

There is no more bitDatePeriod, it's bitDateRange now. :hammer:

[jeremyFreeAgent]

DatePeriod is a holy crap. I think it's a trainee who made it... :school_satchel:

[stephpy]

Yes, let's overwrite it :)