Fix tags and keywords on posts

The tags are appearing with double-commas on the index.

Update the documentation to say that tags and keywords on blog posts
should be written in the markdown as space-delimited lists, rather
than comma-delimited.

Fix the existing posts accordingly.

There are still some glitches with tag handling, which are not fixed
in this commit:

- The tag archive pages are not being generated, so clicking on any
  of the tag links results in a "not found" page.

- All the tags are rendered on the index, but only the first tag is
  rendered in the actual post.

Change-Id: Ifaa8f2b020e1e8beaac4226658b8fd3435afc0de
diff --git a/_posts/2019-02-27-user-summit-gothenburg.md b/_posts/2019-02-27-user-summit-gothenburg.md
index a3d5f2f..980d7cc 100644
--- a/_posts/2019-02-27-user-summit-gothenburg.md
+++ b/_posts/2019-02-27-user-summit-gothenburg.md
@@ -1,7 +1,7 @@
 ---
 title: Gerrit User Summit 2019, 29-30 Aug in Gothenburg (Sweden)
-tags: news, summit, hackathon
-keywords: news, summit, hackathon
+tags: news summit hackathon
+keywords: news summit hackathon
 permalink: 2019-02-27-user-summit-gothenburg.html
 summary: "The Gerrit Community, with the collaboration of Volvo Cars and GerritForge,
 is happy to announce the Gerrit User Summit & Hackathon 2019"
diff --git a/_posts/2019-03-16-user-summit-gothenburg-registration-open.md b/_posts/2019-03-16-user-summit-gothenburg-registration-open.md
index 660db89..0447f9a 100644
--- a/_posts/2019-03-16-user-summit-gothenburg-registration-open.md
+++ b/_posts/2019-03-16-user-summit-gothenburg-registration-open.md
@@ -1,7 +1,7 @@
 ---
 title: Gerrit User Summit 2019 Registration is Open
-tags: news, summit, hackathon
-keywords: news, summit, hackathon
+tags: news summit hackathon
+keywords: news summit hackathon
 permalink: 2019-02-27-user-summit-gothenburg-registration-open.html
 summary: "Registration for the Gerrit User Summit 2019 is now open"
 hide_sidebar: true
diff --git a/pages/site/publishing-gerrit-docs.md b/pages/site/publishing-gerrit-docs.md
index afce48a..f8cf496 100644
--- a/pages/site/publishing-gerrit-docs.md
+++ b/pages/site/publishing-gerrit-docs.md
@@ -183,8 +183,8 @@
     Where:
 
     +  `[TITLE]` is the title of the blog post
-    +  `[TAGS]` is an optional comma-delimited list of tags
-    +  `[KEYWORDS]` is an optional comma-delimited list of keywords
+    +  `[TAGS]` is an optional space-delimited list of tags
+    +  `[KEYWORDS]` is an optional space-delimited list of keywords
     +  `[FILENAME]` is the name of the file
     +  `[SUMMARY]` is a one- to two- sentence description of the post