In TableOfContentsFilter, generate a Table of Contents as a HTML unordered list of links to headers.

  * Add test cases for directly using HTML::Pipeline::TableOfContentsFilter
  * Add test cases for using HTML::Pipeline::TableOfContentsFilter within a HTML::Pipeline
  * Initialize result[:toc] to an empty string in TableOfContentsFilter#call
  * Initialize @toc to an empty string in TableOfContentsFilter#call
  * Set toc as an attr_reader on TableOfContentsFilter
  * Extract adding header anchor to TableOfContentsFilter#add_header_anchor
  * Define TableOfContentsFilter#append_toc for adding a toc item
  * Define TableOfContentsFilter#finalize_toc for wrapping toc items in a container
    * Markup from GitHub Styleguide Styling & CSS Navigation 8.3.1
  * Update TomDoc
  * Update README.md explaining generated Table of Contents
Keep TableOfContentsFilter interface consistent with other filters by removing attr_reader. Also, reduce complexity by removing private methods and keep changes within #call. Finally, implement #build_toc to wrap result[:toc] in an unordered list.
Remove #build_toc and move logic into #call, so all toc logic is within #call
Merge pull request #75 from simeonwillbanks/generated-table-of-contents

Generate Table of Contents