This involves setuid'ing swaylock, which then forks and drops perms on
the parent process. The child process remains root and listens on a pipe
for requests to validate passwords against /etc/shadow.
- Replace char* with static array. Any chars > 1024 will be discarded.
- mlock() password buffer so it can't be written to swap.
- Clear password buffer after auth succeeds or fails.
This is basically the same treatment I gave the 0.15 branch in https://github.com/swaywm/sway/pull/1519
Colors are configured through the command line so that swaylock conforms
to the i3lock fork 'github.com/chrjguill/i3lock-color'. Differences from
it are that one letter options '-r' and '-s' are not implimentend because
'-s' is already used by '--scaling' in swaylock.
This commit also fixed whitespace in 'include/swaylock/swaylock.h' and
changed `parse_color` in 'common/util.h' so that it can accept colors
that do not start with a hash. This was done to keep compatability with
the i3lock fork.
