doc: re-organize golang.org site content

Remove "References" section.
Remove most articles and redirect to blog.golang.org.
Move /ref/spec and /ref/mem to /doc/spec and /doc/mem.
Remove duplicate links from the remaining
"Documents", "The Project", and "Help" pages.
Defer to the wiki for more links and community content.
Update command reference and mention cover tool.
Add "Pop-out" text to the front page.
Pick one of four videos at random to feature on the front page.

Fixes #2547.
Fixes #5561.
Fixes #6321.

R=r, dominik.honnef
CC=golang-dev
https://golang.org/cl/13724043
diff --git a/doc/cmd.html b/doc/cmd.html
index ac54923..b8bdcda 100644
--- a/doc/cmd.html
+++ b/doc/cmd.html
@@ -27,9 +27,9 @@
 </p>
 
 <p>
-Finally, two of the commands, <code>fmt</code> and <code>doc</code>, are also
-installed as regular binaries called <code>gofmt</code> and <code>godoc</code>
-because they are so often referenced.
+Finally the <code>fmt</code> and <code>godoc</code> commands are installed
+as regular binaries called <code>gofmt</code> and <code>godoc</code> because
+they are so often referenced.
 </p>
 
 <p>
@@ -62,6 +62,13 @@
 </tr>
 
 <tr>
+<td><a href="http://godoc.org/code.google.com/p/go.tools/cmd/cover/">cover</a></td>
+<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
+<td>Cover is a program for creating and analyzing the coverage profiles
+generated by <code>"go test -coverprofile"</code>.
+</tr>
+
+<tr>
 <td><a href="/cmd/fix/">fix</a></td>
 <td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
 <td>Fix finds Go programs that use old features of the language and libraries
@@ -69,13 +76,6 @@
 </tr>
 
 <tr>
-<td><a href="/cmd/go/">doc</a></td>
-<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
-<td>Doc extracts and generates documentation for Go packages, it is also available as
-an independent <a href="/cmd/godoc/">godoc</a> command with more general options.</td>
-</tr>
-
-<tr>
 <td><a href="/cmd/go/">fmt</a></td>
 <td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
 <td>Fmt formats Go packages, it is also available as an independent <a href="/cmd/gofmt/">
@@ -83,7 +83,13 @@
 </tr>
 
 <tr>
-<td><a href="/cmd/vet/">vet</a></td>
+<td><a href="http://godoc.org/code.google.com/p/go.tools/cmd/godoc/">godoc</a></td>
+<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
+<td>Godoc extracts and generates documentation for Go packages.</td>
+</tr>
+
+<tr>
+<td><a href="http://godoc.org/code.google.com/p/go.tools/cmd/vet/">vet</a></td>
 <td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
 <td>Vet examines Go source code and reports suspicious constructs, such as Printf
 calls whose arguments do not align with the format string.</td>