Remove markdown links from TOC entries.

e.g., the "Getting Help" chapter has section headings containing
markdown links, which were rendered poorly.

Rakefile

@@ -87,12 +87,17 @@ end
 
 def chapter_toc(content)
   header_re = /^(##) /
+  markdown_link_re = /\[(.*)\](\[.*\]|\(.*\))/
   toc = []
   content = content.split("\n").map do |line|
     if line =~ header_re
       title = line.gsub(header_re, '')
       header = $1
 
+      if title =~ markdown_link_re
+        title = title.gsub(markdown_link_re, '\1')
+      end
+
       # extract id and store it into toc
       id = title.downcase.gsub(/\W/, '_')
       toc_entry = "1. [#{title}](##{id})"