This call takes an input and an output argument and will copy all files
from the input to the output, while minifying the Lua files.

[Matthias Schiffer: simplified definition, added commit message.]

Packages in the openwrt-routing master have adjusted to this upstream
change, so we follow. Also saves a bit of space.

Our build process works similarly to the image builder and doesn't support
the generation of initramfs-based images.

Fixes #616

`make modules` will generate a opkg repository containing kernel modules
matching the kernel of the Gluon images.

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

The upstream builds always use LINUX_RELEASE=1. By setting it to 2 we
ensure that our modules are always preferred as long as our kernel version
is at least as high as the upstream one.

As the Gluon kernel won't be compatible with the OpenWrt upstream anymore,
we don't need the vermagic hack anymore.

The new options allow specifying custom repositories and are evaluated
in an upgrade script, not during build.

This also takes us past the OpenWrt 15.05 final release.

With this change, there are two OpenWrt config files: one for the packages
actually used by Gluon, and one with all kernel modules enabled (like it was
since we removed the static kernel configs). The config with all kernel modules
is only used to generate the kernel configuration (so it is compatible with the
upstream kernel).

This should bring the build times back to what they were before the static
configs were removed.

With a backported patch from the OpenWrt trunk, it is now easy to generate an
equivalent configuration using CONFIG_ALL_KMODS.

The build will take a bit longer because all kernel module packages are actually
built even when they are not included in the image, but adding new targets
becomes a lot easier.

Also, related documentation updates and fixes.

Don't set ar71xx-generic target by default, generate manifest for all built
targets.

Also add some patches from OpenWrt trunk and use the CT ath10k firmware.

mpc85xx and x86 are unchanged since rc3.

Updating OpenWrt accidentally enabled this option.

They aren't used by default and can simply be installed through opkg if needed.