Add sleep method (#628)

Author: cstjean

src/Unitful.jl

@@ -16,6 +16,7 @@ import Base: length, float, last, one, oneunit, zero, range
 import Base: getindex, eltype, step, last, first, frexp
 import Base: Integer, Rational, typemin, typemax
 import Base: steprange_last, unsigned
+import Base: sleep
 @static if VERSION ≥ v"1.7.0-DEV.119"
     import Base: isunordered
 end

src/dates.jl

@@ -186,3 +186,5 @@ end
 
 isapprox(x::AbstractArray{Dates.CompoundPeriod}, y::AbstractArray{<:AbstractQuantity};
          kwargs...) = isapprox(y, x; kwargs...)
+
+sleep(x::AbstractQuantity) = sleep(ustrip(s, x))

test/dates.jl

@@ -783,4 +783,6 @@
         @test_throws ErrorException promote(1u"m", Second(1))
         @test_throws ErrorException promote(Day(1), 3u"T")
     end
+
+    sleep(10u"ms")    # not tested explicitly, because sleep doesn't come with guarantees
 end