Extension to support IrrationalConstants

[Kolaru]

Reported from JuliaIntervals/IntervalRootFinding.jl#225

Currently, we are not supporting irrational numbers defined in IrraitonalConstants.jl

julia> using IntervalArithmetic, IrrationalConstants

julia> interval(twoπ)
ERROR: ArgumentError: only irrationals from MathConstants are supported

It would be relatively straightforward to support it, by defining our own interval rounding for all of their constants, just like we do for the golden ratio

IntervalArithmetic.jl/src/intervals/construction.jl

Lines 101 to 104 in 544c000

	_round(::Type{T}, ::Irrational{:φ}, r::RoundingMode{:Down}) where {T<:NumTypes} =
	__round(T, inf((bareinterval(BigFloat, 1) + sqrt(bareinterval(BigFloat, 5))) / bareinterval(BigFloat, 2)), r)
	_round(::Type{T}, ::Irrational{:φ}, r::RoundingMode{:Up}) where {T<:NumTypes} =
	__round(T, sup((bareinterval(BigFloat, 1) + sqrt(bareinterval(BigFloat, 5))) / bareinterval(BigFloat, 2)), r)