Get docstring without @doc to avoid error when compiling (#116)

* Get docstring without @doc to avoid error when compiling

Fixes #113.

* Add comment with link to upstream @doc issue

src/metrics.jl

@@ -332,10 +332,13 @@ function eval_end(dist::RenyiDivergence, s::Tuple{T,T,T,T}) where {T <: Real}
     end
 end
 
-# Combine docs with RenyiDivergence
-@doc (@doc RenyiDivergence) renyi_divergence
-
 renyi_divergence(a::AbstractArray, b::AbstractArray, q::Real) = evaluate(RenyiDivergence(q), a, b)
+# Combine docs with RenyiDivergence. Fetching the docstring with @doc causes
+# problems during package compilation; see
+# https://github.com/JuliaLang/julia/issues/31640
+let docstring = Base.Docs.getdoc(RenyiDivergence)
+    @doc docstring renyi_divergence
+end
 
 # JSDivergence
 @inline function eval_op(::JSDivergence, ai::T, bi::T) where {T}