Document that grad and j′vp return tuples. (#220)

* Document that grad and j′vp return tuples.

Fixes #219.

* bump patch version

Author: tpapp

Project.toml

@@ -1,6 +1,6 @@
 name = "FiniteDifferences"
 uuid = "26cc04aa-876d-5657-8c51-4c34ba976000"
-version = "0.12.26"
+version = "0.12.27"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/grad.jl

@@ -66,6 +66,8 @@ end
     j′vp(fdm, f, ȳ, x...)
 
 Compute an adjoint with any types of arguments `x` for which [`to_vec`](@ref) is defined.
+
+Return tuple of gradients, one for each argument.
 """
 function j′vp(fdm, f, ȳ, x)
     x_vec, vec_to_x = to_vec(x)
@@ -84,5 +86,7 @@ end
     grad(fdm, f, xs...)
 
 Compute the gradient of `f` for any `xs` for which [`to_vec`](@ref) is defined.
+
+Return tuple of gradients, one for each argument.
 """
 grad(fdm, f, xs...) = j′vp(fdm, f, 1, xs...)  # `j′vp` with seed of 1