doc: fix id attributes in links to godoc

CL6449105 changed godoc id attributes to ensure uniqueness.
This CL updates links to godoc pages in documents that used
the old id attributes.

R=golang-dev, dsymonds
CC=golang-dev, speter.go1
https://golang.org/cl/7015051

doc/articles/godoc_documenting_go_code.html

@@ -83,7 +83,7 @@ godoc's output, with one notable exception. Top-level comments that begin with
 the word <code>"BUG(who)"</code> are recognized as known bugs, and included in
 the "Bugs" section of the package documentation. The "who" part should be the
 user name of someone who could provide more information. For example, this is a
-known issue from the <a href="/pkg/bytes/#bugs"><code>bytes</code></a> package:
+known issue from the <a href="/pkg/bytes/#pkg-bugs"><code>bytes</code></a> package:
 </p>
 
 <pre>

doc/go1.html

@@ -1676,7 +1676,7 @@ instead of a <code>Visitor</code> interface value.
 The <code>WalkFunc</code> function will be called even for files or directories that could not be opened;
 in such cases the error argument will describe the failure.
 If a directory's contents are to be skipped,
-the function should return the value <a href="/pkg/path/filepath/#variables"><code>filepath.SkipDir</code></a>
+the function should return the value <a href="/pkg/path/filepath/#pkg-variables"><code>filepath.SkipDir</code></a>
 </p>
 
 {{code "/doc/progs/go1.go" `/STARTWALK/` `/ENDWALK/`}}
@@ -1865,7 +1865,7 @@ made easier with the new structure of the packages.
 The imports will be updated by fix tool.
 Single-template uses will be otherwise be largely unaffected.
 Code that uses multiple templates in concert will need to be updated by hand.
-The <a href="/pkg/text/template/#examples">examples</a> in
+The <a href="/pkg/text/template/#pkg-examples">examples</a> in
 the documentation for <code>text/template</code> can provide guidance.
 </p>