Disabling `exhale` because it is just overloading things right now.

Hidden in this commit are a couple of other items:
* Enable .md documents for CONTRIBUTING.md to avoid same content not on
  docs.beagleboard.org
* Added graphviz to the venv setup, but that doesn't do much as I think
  it was already there

Update License Terms grid

See merge request docs/docs.beagleboard.io!68

Bring back ch06 as it has needed details we need to flesh out.

This reverts commit 526e8e6d.

Gateware design overview and version retrieval

See merge request beaglev-fire/docs!1