Replace occurences of ar71xx with ath79. Remove references of ar71xx
targets which are not relevant anymore.

Explains the behaviour when DATE is either in the future or in the past
and hints at how the firmware rollout can be controlled using the
PRIORITY variable.

Co-Authored-By: Martin Weinelt <martin@darmstadt.freifunk.net>

Adding the fact that GLUON_RELEASE is needed with 'make manifest'
if it is used with 'make'.

This fact was mentioned in the v2017.1 release notes but is not (clearly)
mentioned inside other parts of the documentation.

Signed-off-by: Chrissi^ <chris@tinyhost.de>

[Matthias Schiffer: minor rewording]

fix typo and express sentence regarding update priority clearer

We'll soon have other output besides the images, having a single directory
for all output makes sense.

the command autoupdate not work, so a fix smal fix necessary

docs: Basic site documentation
docs: Basic autoupdater documentation
docs: minimal autoupdater info
docs: bump version to 2014.2

Closes #114