Add mention of join() to the section of the manual about strings

[nalimilan]

This is one of the very useful functions which can be hard to find,
and very similar to repeat().

[ivarne]

Looks good to me.

[ivarne]

By the way, none of the functions in manual/strings/ are clickable links. I tried to add :func: before the names, but it did not produce clickable links when generating locally with make html. Does anyone know what it would take?

[jiahao]

@ivarne Sphinx doesn't know which namespace to use. You need to add .. currentmodule:: Base near the top of the file.

I pushed the necessary change to strings.rst in 6655241, you can go ahead and change the rest of the functions to be linkable.

[tkelman]

docfix, @JuliaBackports?

[ivarne]

Thanks @jiahao! I don't have time the next week or so, but will eventually get to it if the backport pending label stays on.

[tkelman]

backported in 4767284 (and @jiahao's followup in 7852bb0)

[ivarne]

Fixed more links in bf5a404 and backported in b296937

[nalimilan]

Thanks!