Allow specification of sorting alg

Using ThreadsX.QuickSort gives about 2x performance improvement using 4 
threads

Author: baggepinnen

src/AlphaStableDistributions.jl

@@ -66,8 +66,8 @@ Fit a symmetric α stable distribution to data.
 c is computed based on Fama & Roll (1971) fractile.
 δ is the 50% trimmed mean of the sample.
 """
-function Distributions.fit(d::Type{<:AlphaStable}, x)
-    sx = sort(x)
+function Distributions.fit(d::Type{<:AlphaStable}, x, alg=QuickSort)
+    sx = sort(x, alg=alg)
     δ = mean(@view(sx[end÷4:(3*end)÷4]))
     p = quantile.(Ref(sx), (0.05, 0.25, 0.28, 0.72, 0.75, 0.95), sorted=true)
     c = (p[4]-p[3])/1.654