Now that the content in `guides` is all of the edx-platform docs, move
them all into the top-level docs directory to reduce confusion.
BREAKING CHANGE: Guides are now just docs. This will require updating
the publishing settings so that RTD looks for the conf in a different
location.
This is part of a larger effort to split packages out into independent,
composable, PyPI installable Python packages.
While this package itself isn't monumental, it represents the bottom of
the dependecy tree and can be split out before any other packages.
