Add more twitter integration

- If the blog author's twitter ID is specified, add a small twitter
bird after the author's name
- Add the @JuliaLanguage twitter handle for the twitter site metadata

_layout/head.html

@@ -58,7 +58,7 @@ <h3>
   {{isdef published}} <span style="font-weight: lighter;"> {{fill published}} </span>
 	|
 	{{end}}
-	{{isdef author}} <span style="font-weight: bold;">{{fill author}}</span> {{end}}
+	{{isdef author}} <span style="font-weight: bold;">{{fill author}}{{author_twitter}}</span> {{end}}
   <!-- assumption that only one of the two is defined -->
   {{isdef authors}} <span style="font-weight: bold;">{{fill authors}} </span> {{end}}
   </h3>

_layout/meta.html

@@ -3,3 +3,4 @@
 <meta http-equiv="x-ua-compatible" content="ie=edge">
 <meta name="author" content="Jeff Bezanson, Stefan Karpinski, Viral Shah, Alan Edelman, et al.">
 <meta name="description" content="The official website for the Julia Language. Julia is a language that is fast, dynamic, easy to use, and open source. Click here to learn more.">
+<meta name="twitter:site:id" content="1237720952"> <!-- @JuliaLanguage -->

blog/2020/09/rr-memory-magic.md

@@ -1,10 +1,12 @@
 +++
-authors = "Keno Fischer"
+author = "Keno Fischer"
 published = "24 September 2020"
 title = "Remotely Debugging Faulty Memory - an rr case study"
 rss = """Since the release of Julia 1.5 we've gotten lots of rr traces. This tells the story of a particularly interesting one."""
 meta = [
     ("property", "og:image", "https://julialang.org/assets/blog/2020-09-23-rr-memory/faulty-mem.jpg"),
+    ("name", "twitter:creator:id", "4922348584"),
+    ("name", "twitter:card", "summary_large_image")
     ]
 +++
 

utils.jl

@@ -151,3 +151,19 @@ function hfun_redirect(url)
     """
     return s
 end
+
+"""
+    {{author_twitter}}
+"""
+function hfun_author_twitter()
+    meta = locvar(:meta)
+    if meta !== nothing
+        for (kind, tag, value) in meta
+            if kind == "name" && tag == "twitter:creator:id"
+                return " <a href=\"https://twitter.com/intent/user?user_id=$value\"><img src=\"/assets/infra/twitter_16.png\"/></a>"
+            end
+        end
+    end
+    return ""
+end
+