Change heading anchors to kramdown style ids

[cjohnson19]

Description of changes:

The anchor links which kramdown generates in the table of contents are based on the heading's HTML content and add an id to the header itself. Since it uses the HTML content, this duplicated the anchor into the toc. Links in the docs which referred to these anchors would then go to the table of contents instead of the heading itself.

For example, the headings as they are now generate in the table of contents to look like:

<li>
  <a href="#features-of-cedar" id="markdown-toc-features-of-cedar">Features of Cedar</a>
  <a name="feature-overview"></a>
</li>

While the heading is:

<h2 id="features-of-cedar">
<!-- Content omitted -->
Features of Cedar<a name="feature-overview"></a>
</h2>

This change specifies the anchors manually to prevent kramdown creating new ones -- preventing the double destination problem.

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[AMZ-brandon]

Hi Chase! Thanks for the contribution, and apologies for the delay. I'm evaluating your changes in my test environment and will come back shortly.

[cjohnson19]

Hi Chase! Thanks for the contribution, and apologies for the delay. I'm evaluating your changes in my test environment and will come back shortly.

No problem at all! Take your time and let me know if you have any questions / concerns I could address. Thanks for fixing those merge conflicts.

[AMZ-brandon]

I'm satisfied that this is a better system for implementing the anchors. Thanks again for the contribution!