Added command line argument '-t' to specify the length of time (in
milliseconds) over which to interpolate brightness changes. The time
between each brightness step is still unconfigurable at 10ms.

Forces brightness to always change gradually in 20 steps, with a delay of 10 milliseconds between each step. This is a preliminary proof-of-concept until both values are made configurable.

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

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

Co-Authored-By: TheJakeSchmidt <TheJakeSchmidt@users.noreply.github.com>

Introduce the concept of a float-typed value in the context, for commands
like -T that don't work with percentages/raw values.

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

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>

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

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

- Use version from configure script
- Simplify usage text for accessibility, only one command at a time
- Simplify terminology, we have commands and options to commands

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

Without this patch -O and -I are not supported anymore and lead to an
error.

- Use NAME_MAX and PATH_MAX instead of hardcoded values
- Allow paths to be longer than 256 chars
- Check pointers everywhere
- Use strncpy/snprintf instead of strcpy/sprintf
- Validate controllers' name (-s flag + a very long name -> bad things happening)
- Get rid of globals for dir iteration

- Rewrite of all clamp operations
- Get rid of unreachable code (the 'else' in the last chunk)

Now we can save, restore, get [max] brightness etc. for both screen
and keyboard controllers

This function was:
- Reading values from the controller
- Checking write permission even when we just want reading values
- Checking the mincap file instead of the actual controller

The last one is also true for other functions using
'light_getBrightness'.
This commit fixes that.