[Feature Request] want to use another months in beginning_of_quarter and end_of_quarter

[Shinohara Teruki]

Hello,

The current implementation of `beginning_of_quarter` and `end_of_quarter` uses fixed months to find the (beginning or end) of quarter.

I think it's useful to be able to change the default value because (beginning or end) of quarter changes according to the situation.

How about this implementation?

https://github.com/ts-3156/rails/commit/c59b9e327c69fe226941b1dbfcd81e2d0046b5b2