Replace IRC with Slack (#132)

Our Slack community has been much more active than IRC for some time,
and we would like to centralize.

Gemfile.lock

@@ -233,6 +233,10 @@ GEM
     rubyzip (2.3.0)
     safe_yaml (1.0.5)
     sass (3.7.4)
+      sass-listen (~> 4.0.0)
+    sass-listen (4.0.0)
+      rb-fsevent (~> 0.9, >= 0.9.4)
+      rb-inotify (~> 0.9, >= 0.9.7)
     sawyer (0.8.2)
       addressable (>= 2.3.5)
       faraday (> 0.8, < 2.0)
@@ -258,4 +262,4 @@ DEPENDENCIES
   github-pages
 
 BUNDLED WITH
-   2.1.4
+   2.2.16

_data/nav.yml

@@ -22,16 +22,12 @@
   href: https://www.facebook.com/hhvm/
   category: external
 
-- title: Twitter
-  href: https://twitter.com/HipHopVM
-  category: external
-
-- title: IRC
-  href: http://webchat.freenode.net/?channels=hhvm
+- title: Slack
+  href: /slack/
   category: external
 
-- title: Module Support
-  href: http://hhvm.h4cc.de/
+- title: Twitter
+  href: https://twitter.com/HipHopVM
   category: external
 
 # Use external for external links not associated with the paths of the current site.

_data/nav_docs.yml

@@ -1,7 +1,3 @@
-- title: Grouping 1
-  items:
-  - id: hello-world
-
 # n title:, 1 items: per title:, n id: per items:
 # - title: A
 #   items:

slack.md

@@ -0,0 +1,11 @@
+---
+layout: redirect
+title: Hack and HHVM Slack
+id: slack
+destination: https://forms.gle/io5oYV1CunwZUC2EA
+---
+
+The Hack and HHVM Slack community is at
+[https://hacklang.slack.com](https://hacklang.slack.com); to join, please
+[read our code of conduct](https://opensource.facebook.com/code-of-conduct) then
+[request an invitation](https://forms.gle/io5oYV1CunwZUC2EA).