Optimize `Range#initialize` for `Bignum`, `Float`, `String`, and `Symbol`

[kyanagi]

In range_init, a check is performed to determine if beg and end are comparable. This check is skipped when both of them are Fixnum. By treating more classes in this manner, we can speed up Range#new.

benchmark

Iteration per second (i/s)

	master	PR
Range.new(0, 5)	11.964M	11.976M
	-	1.00x
Range.new(0, bignum)	7.451M	11.627M
	-	1.56x
Range.new(0, 5.5)	9.176M	11.870M
	-	1.29x
Range.new('a', 'z')	6.959M	8.088M
	-	1.16x
Range.new(:a, :z)	8.583M	11.816M
	-	1.38x
Range.new(0, nil)	11.956M	11.933M
	1.00x	-
Range.new(date1, date2)	8.296M	8.244M
	1.01x	-
Range.new(time1, time2)	9.140M	9.008M
	1.01x	-