upgrade to newer PulseAudio crate dependency

requires adding dependency on libpulse-simple-sys since the PulseAudio
simple components were moved to their own crate (the original version
did not stick to the one crate per one system library rule).

this fixes the licensing compatibility issue discussed in #539 ([1])
(the original v0.0.0 was LGPL-3.0 licensed, while v1.11 onwards are
'MIT OR Apache-2.0').

[1]: https://github.com/librespot-org/librespot/issues/539

playback/src/audio_backend/pulseaudio.rs

@@ -1,6 +1,7 @@
 use super::{Open, Sink};
 use libc;
 use libpulse_sys::*;
+use libpulse_simple_sys::*;
 use std::ffi::CStr;
 use std::ffi::CString;
 use std::io;