Update debian packaging

Seeing as light supports at least two different GNU/Linux distributions
it seems prudent to not claim 'package:' for Debian packages.  This has
the added benefit of adding easy build targets for RedHat/Fedora, Arch,
and others.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

- Bump debhlper compat to >= 10 (Stretch)
- Update Standards-Version field, we seem to be compatible
- Update package Description filed, lintian complains of empty body
- Update changelog date and drop GitHub issue reference, confuses lintian

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Rewrite codebase, add device-system pewpew

Respect XDG_CACHE_HOME

The XDG Base Directory specification [1] demands that there should be a
"single base directory relative to which user-specific non-essential
(cached) data should be written". Light currently makes use of such a
cache directory, but hardcodes the default "$HOME/.cache".

In order to enable users to specify a custom cache directory, respect
this convention and use the "$XDG_CACHE_HOME" environment variable if it
is set. If it is not set, fall back to "$HOME/.cache".

[1] https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

Brillo merges

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

ChangeLog updates, Debian packaging support

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

We may need to drop the $prefix to the udev rules from configure.ac

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Doc updates

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Add --with-udev[=PATH] to configure script, for non-SUID root operation

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

When light is installed in the non-SUID root mode it cannot write to
/etc/light anymore, so we set up a ~/.cache/light instead.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

This patch adds support for installing the 90-backlight.rules to gain
privileges to the kernel sysfs files.  By default the classic SUID root
mode is used and the rules file is not installed.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Add Fedora installation instructions

Coding style

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Misc