docs: Add top level page for language bindings.

Lists API client bindings/libraries/wrappers and makes a distinction
between official core projects and community projects.

Tweaked by tabbott to sort the community and outdated libraries, and
restructure how we talk about other projects.

Fixes #2093.

templates/zerver/api/client-libraries.md

@@ -0,0 +1,59 @@
+# Client libraries
+
+These API client libraries make it easy to work with Zulip's REST API
+in your favorite language.
+
+## Official libraries
+
+These libraries are maintained by members of the Zulip core team.  The
+Python library is the most complete and best documented.
+
+* [Python](https://github.com/zulip/python-zulip-api)
+* [JavaScript](https://github.com/zulip/zulip-js)
+
+## User maintained libraries
+
+The Zulip core team doesn't have the resources to maintain
+high-quality libraries for every programming language.  We've
+collected a list of user-maintained libraries for popular languages:
+
+* [Clojure](https://github.com/thieman/clojure-zulip)
+* [C#](https://github.com/zulip/zulip-csharp)
+* [Go](https://github.com/ifo/gozulipbot)
+* [Java](https://github.com/taliox/zulip-java-rest)
+* [Kotlin](https://gitlab.com/ppiag/kzulip)
+* [PHP](https://github.com/mrferos/zulip-php-client)
+* [Ruby](https://github.com/raws/wonder-llama)
+* [Swift](https://github.com/zulip/swift-zulip-api)
+
+### Contributing
+
+Contributing to improve language libraries is appreciated, as is
+writing new ones.  If you actively maintain a Zulip language binding
+and would like it to be listed here (or would like to collaborate with
+us in making it an official library), post in [this
+topic][integrations-thread] on
+[chat.zulip.org](https://chat.zulip.org) or submit a pull request
+[updating this
+page](https://zulip.readthedocs.io/en/latest/documentation/api.html).
+
+[integrations-thread]: https://chat.zulip.org/#narrow/stream/127-integrations/topic/API.20client.20libraries/
+
+### Outdated
+
+!!! tip ""
+    The following projects are not actively maintained.  Since
+    Zulip's core APIs have been stable for 5 years, even very
+    old libraries can be useful.
+
+* [Lua](https://github.com/deckycoss/zulua)
+* [Erlang](https://github.com/femnad/tuplre)
+* [PHP](https://github.com/federicoq/zulip-php)
+* [Go](https://github.com/decached/go-zulip)
+* [Haskell](https://github.com/yamadapc/hzulip)
+* [Chicken Scheme](https://github.com/yamadapc/zulip-scheme)
+* [Scala](https://github.com/cqfd/zulip-scala)
+* [EventMachine](https://github.com/cqfd/zulip_machine)
+* [Ruby](https://github.com/verg/zulip-rb)
+* [Perl](https://github.com/Stantheman/WebService-Zulip)
+* [.Net](https://github.com/Shayan-To/ZulipClientApi)

templates/zerver/api/installation-instructions.md

@@ -37,3 +37,5 @@ npm install zulip-js
 No download required!
 
 {end_tabs}
+
+See also the [unofficial client libraries](#client-libraries) for many languages.

templates/zerver/api/rest.md

@@ -8,7 +8,8 @@ you can do in Zulip, you can do with Zulip's REST API.  To use this API:
   using the API to interact with
   your own account (e.g. exporting your personal message history).
 * Choose what language you'd like to use.  You can download the
-  [Python or JavaScript bindings](/api/installation-instructions), or
+  [Python or JavaScript bindings](/api/installation-instructions), projects in
+  [other languages](/api/client-libraries), or
   just make HTTP requests with your favorite programming language.  If
   you're making your own HTTP requests, you'll want to send the
   appropriate HTTP Basic Authentication headers; see each endpoint's

templates/zerver/api/sidebar_index.md

@@ -19,5 +19,6 @@
 * [API keys](/api/api-keys)
 * [Configuring the Python bindings](/api/configuring-python-bindings)
 * [Error handling](/api/rest-error-handling)
+* [Client Libraries](/api/client-libraries)
 
 {!rest-endpoints.md!}