I am extending the `Base.binomial`

which assumes two integer arguments to two complex arguments in `SpecialFunctions`

.

Now, I have problems documenting it. Currently it is implemented via

```
"""
binomial(x, y)
Generalized binomial coefficient for complex arguments
``{x \\choose y} = \\frac{1}{(x+1) \\Beta(x-y+1,y+1)}``
for ``x, y \\ \\mathbb{C}``.
External links: [Wikipedia](https://en.wikipedia.org/wiki/Binomial_coefficient#Two_real_or_complex_valued_arguments)
See also [`beta(a,b)`](@ref SpecialFunctions.beta).
"""
Base.binomial(x::Number, y::Number) = inv((x+1) * beta(x-y+1, y+1))
```

The Documenter.jl script throws tons of warnings wrt to various functions. The warnings for binomial are

```
$ julia docs/make.jl
...
┌ Warning: no docs found for 'Base.binomial' in `@docs` block in src/functions_list.md:7-73
...
┌ Warning: no doc found for reference '[`Base.binomial`](@ref)' in src/functions_overview.md.
└ @ Documenter.CrossReferences ~/.julia/packages/Documenter/FuXcO/src/CrossReferences.jl:160
...
┌ Warning: invalid local link: unresolved path in functions_list.md
│ link.text =
│ 1-element Array{Any,1}:
│ Markdown.Code("", "binomial")
│ link.url = "@ref"
└ @ Documenter.Writers.HTMLWriter ~/.julia/packages/Documenter/FuXcO/src/Writers/HTMLWriter.jl:1823
...
┌ Warning: invalid local link: unresolved path in functions_overview.md
│ link.text =
│ 1-element Array{Any,1}:
│ Markdown.Code("", "binomial(x,y)")
│ link.url = "@ref Base.binomial"
└ @ Documenter.Writers.HTMLWriter ~/.julia/packages/Documenter/FuXcO/src/Writers/HTMLWriter.jl:1823
...
```

I truncated the output but pasted the whole output on pastebin.

I am generally unsure how documenting an extended function (type piracy?) is done. Furthermore, why are all those warnings thrown? Is there something off with the documentation process in SpecialFunctions or is it a bug in Documenter.jl? I mean other functions which should be documented correctly, e.g. `loggamma`

, also throw warnings…

This is in relation to this pr on github.