What we really want is to either output to WM_NAME or stdout. If we want
just one single line, we do slstatus | head -n 1.

d-flag: There's no need for that, use the &-operator or fork+exec in a
        non-shell-context. In the latter case you get the PID for free.
v-flag: If you want to find out which version of a package is installed,
        consult your package manager. That's his job.

We also change the semantics of -v to only return the version
information.
There is now no need for usage() to exit with anything other than 1.

According to https://opensource.org/licenses/ISC

A file outside the repository (.git/info/exclude) can replace this and
suits better for this usecase.

On success, fgets always terminates the result.

If fgets succeeds, then the resulting char array is always
terminated by a '\0'. No need to keep extra space, therefore
sizeof(buf) is the correct argument.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>

Fixed out of boundary write on long lines.

The terminating nul character ('\0') could be written outside the boundary of
the buffer which is used to read characters. If "sizeof(buffer)" characters
are read, the resulting value must not be used as index, because that's an off
by one.

Read sizeof(buffer)-1 bytes instead.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>

refactor vol_perc to not depend on alsa libraries