Truncated quotient and remainder

[HertzDevil]

Number has a #divmod method, which returns the floored quotient (#//) and the modulus (#%) as a 2-tuple:

crystal/src/number.cr

Lines 217 to 219 in 791b0e4

	def divmod(number)
	{(self // number).floor, self % number}
	end

There is no counterpart for the truncated quotient (#tdiv) and remainder (#remainder). Two examples in the standard library are:

crystal/src/int.cr

Lines 667 to 668 in 791b0e4

	ary << num.remainder(base).to_i
	num = num.tdiv(base)

crystal/src/time/span.cr

Lines 68 to 69 in 791b0e4

	@seconds = seconds.to_i64 + nanoseconds.tdiv(NANOSECONDS_PER_SECOND).to_i64
	@nanoseconds = nanoseconds.remainder(NANOSECONDS_PER_SECOND).to_i32

BigInt also has a specialized function for computing both results together, similar to its current #divmod override. I think we should add such a method for completeness. In other languages:

• C/C++: div, ldiv, lldiv, imaxdiv (there is no #divmod equivalent)
• C#: System.Math.DivRem (there is no #divmod equivalent)
• Java: java.math.BigInteger.divideAndRemainder (there is no #divmod equivalent)
• Haskell: quotRem
• Python, Ruby: only divmod is present

If we want to emphasize the similarity with the floored version, #tdivmod is also a possible candidate.