bump version to 1.6

https://git.suckless.org/slock/commit/e3fb34364ed2c53b21edde07ac17560a601783a9.html

quick cancel: allow cancelling by key press in addition to mouse movement ref. #11

simplify post-lock cmd and die if it fails

this patch does two things:

0. simplify the code by using posix_spawn()
1. unify the behavior of what happens if the post-lock cmd fails.

currently, if `fork()` fails, slock will die without locking the screen.
HOWEVER if `execvp()` fails it prints a message to stderr (which the
user cannot see since the screen has been locked already) and only exits
the child while the parent locks the screen.

to reproduce:

	# slock some_bin_that_doesnt_exist

this behavior is inconsistent, if the idea is that post-lock cmd is
_not_ important then we shouldn't `die()` on `fork()` failure either.
and if we assume that the post-lock cmd _is_ important, then we should
die on exec failure as well.

this patch assumes the latter and calls `die()` if `posix_spawn()`
fails.

ref.
https://git.suckless.org/slock/commit/a70d5d2429abf8dcb70a8817990975dc9a621d27.html

slock.1: use standard wording for options

Remove the OPTIONS section and add an EXIT STATUS section.

ref.
https://git.suckless.org/slock/commit/a34d8fb4327bbb1afd92e7527c53fcaad547a495.html

write version to stdout like the man page says

ref.
https://git.suckless.org/slock/commit/e8bca65d629a4faa89439c9f0e599efb5a259573.html

slock.1: improve man page

* Fix all lint warnings.
* Remove "Op Ar arg..." in the description. It looks ugly.
* No need to set -offset left for .Bd literal.

ref.
https://git.suckless.org/slock/commit/ca6f30f621c1195b577ace7a14b9037fab0dab91.html

config.mk: no need to set CC

ref.
https://git.suckless.org/slock/commit/2fec14c567411b939e717c380d8b4460d462b146.html

Makefile: be verbose and remove options

Some things to improve at some point:

* Respect system/packaging CFLAGS/LDFLAGS (don't hardcode -Os -Wall -pedantic,
  -s, etc).

ref.
https://git.suckless.org/slock/commit/5678764412873baa62e1536f0622d6a7cec62181.html

update LICENSE

ref.
https://git.suckless.org/slock/commit/aecfb3f6803bc2e7a5478aeb4f3390cbaaa563c7.html

Bump to 4f04554.

Makefile: explicit_bzero.c was copied twice (GNU make gives a warning)

bump version to 1.5

Ref.
https://git.suckless.org/slock/commit/265704d73647e0d4823126bbb7ddde1d415a618d.html
https://git.suckless.org/slock/commit/4f045545a25cc02c64bfc08d27ed2ccecb962292.html

Merge pull request #8 from herrwusel/pam_consistant

Consistent unlock styles with pam and blur patches

Consistent unlock styles with pam and blur patches

config.mk: adding reference to -D_NETBSD_SOURCE and -D_BSD_SOURCE

Adding background image patch

Proposed change to avoid high CPU usage ref. #7

Fix for secret password patch compilation error ref. #6

Comment out dependencies by default

dwmlogo: avoid defining BACKGROUND colour if BLUR_PIXELATED_SCREEN_PATCH is enabled ref. #5

Adding dwmlogo patch ref. #5

Adding auto-timeout patch