Remove docs directory and tweak main page

We no longer have any content in `docs`. Remove this directory, tweaking
links where possible to relevant locations. As part of this, make sure the
new `guides` and `architecture` sections are linked from the main page.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/_index.md

@@ -75,8 +75,9 @@ Apertis provides a number of pre-built images for Intel (64-bit) and ARM (32-bit
 * [Download the current images]( {{< ref "/images.md" >}} )
 * [Source code](https://gitlab.apertis.org)
 * [Mailing lists](https://lists.apertis.org/)
+* [Architectural documentation]( {{< ref "/architecture" >}}) 
+* [Development guides]( {{< ref "/guides" >}} )
 * [Development guidelines]( {{< ref "/guidelines/_index.md" >}} )
 * [Concept designs]( {{< ref "concepts" >}} )
 * [Supported APIs](https://developer.apertis.org/latest/apis.html)
 * [App developer portal](https://developer.apertis.org)
-* [Further documentation]( {{< ref "docs" >}} )

content/docs/_index.md

-+++
-date = "2015-04-07"
-weight = 100
-
-title = "Documentation"
-
-aliases = [
-    "/old-wiki/Docs"
-]
-+++

content/release/14.12/releasenotes.md

@@ -102,7 +102,7 @@ The designs are available [here](https://designs.apertis.org/).
 
 Updated documentation for the features developed during the project.
 
-[Here]( {{< ref "docs" >}} ) is a list of the available
+[Here]() is a list of the available
 documentation.
 
 ## Build and Integration