Merge fuel-dev docs into fuel-docs repo and web page

We propose merging the fuel-web (fuel-dev) documentation into the fuel-docs repo so we have a single repository and web page for the Fuel documentation. This improves the customer experience by providing a smoother "learning path" from novice user to sophisticated user/admin to developer; it also streamlines our internal processes by having a single doc repo with one set of build tools and processes. Initially, the fuel-web/docs/develop guide becomes the "Developer Guide" in fuel-docs. The autodocs tool will continue to be run in the fuel-web repo; the build tools then need to copy the built doc source into fuel-docs for final processing. They will appear under the "Fuel API Reference" title on the fuel-docs web page.