xfun 0.37

• Added a function is_arm64() to test the CPU type (thanks, @AlbanSagouis, #72).

• Started deprecating xfun::isFALSE() in favor of base::isFALSE() for R >= 3.5.0 (thanks, @mmaechler, #66); isFALSE() will eventually be removed from xfun when we do not need to support R < 3.5.0.