Make easier to test with time.Now as a config about now HOT 2 OPEN

My purpose is to can test a function that use now.BeginingOf..., not to use now inside a test.
For example we cannot add a test in this package for the function now.BeginningOfWeek(). I mean it's an usual issue to test a function that use the current datetime...

from now.

It's difficult to test function in main like now.BeginingOf... because it use time.Now()

For testing purposes, one can just use the With free function which returns an instance of Now that has the same family of BeginningOf functions.

now.With(time.Date(2021, 1, 1, 0, 0, 0, 0, time.Local)).BeginningOfWeek()

Having said that, the ability the override such stuff exists in many Golang libraries via conventional OverrideFooFunc facilities, which seems like a good addition to this library but I do not see it bringing much of a value testing wise.

Cheers.

from now.