cmake: replace included libplist with system library

The system version is regularly updated, so use that instead.  Users now
need to

	sudo apt install libplist-dev

in order to build.

CMakeLists.txt

@@ -7,7 +7,6 @@ set (CMAKE_CXX_STANDARD 11)
 add_subdirectory(lib/curve25519)
 add_subdirectory(lib/ed25519)
 add_subdirectory(lib/playfair)
-add_subdirectory(lib/plist)
 add_subdirectory(lib)
 add_subdirectory(renderers)
 

README.md

@@ -32,6 +32,7 @@ The following packages are required for building on Raspbian:
 
 * **cmake** (for the build system)
 * **libavahi-compat-libdnssd-dev** (for the bonjour registration)
+* **libplist-dev** (for plist handling)
 * **libssl-dev** (for crypto primitives)
 * **ilclient** and Broadcom's OpenMAX stack as present in `/opt/vc` in Raspbian.
 
@@ -45,6 +46,7 @@ For building on a fresh Raspbian Stretch or Buster install, these steps should b
 ```bash
 sudo apt-get install cmake
 sudo apt-get install libavahi-compat-libdnssd-dev
+sudo apt-get install libplist-dev
 sudo apt-get install libssl-dev
 mkdir build
 cd build
@@ -90,7 +92,6 @@ The code in this repository accumulated from various sources over time. Here is
 * **dsafa22**: Created an [AirPlay 2 mirroring server](https://github.com/dsafa22/AirplayServer)(seems gone now) for Android based on ShairPlay. This project is basically a port of dsafa22's code to the Raspberry Pi, utilizing OpenMAX and OpenSSL for better performance on the Pi. All code in `lib/` concerning mirroring is dsafa22's work. License: GNU LGPLv2.1+
 * **Juho Vähä-Herttua** and contributors: Created an AirPlay audio server called [ShairPlay](https://github.com/juhovh/shairplay), including support for Fairplay based on PlayFair. Most of the code in `lib/` originally stems from this project. License: GNU LGPLv2.1+
 * **EstebanKubata**: Created a FairPlay library called [PlayFair](https://github.com/EstebanKubata/playfair). Located in the `lib/playfair` folder. License: GNU GPL
-* **Jonathan Beck, Nikias Bassen** and contributors: Created a library for plist handling called [libplist](https://github.com/libimobiledevice/libplist). Located in the `lib/plist` folder. License: GNU LGPLv2.1+
 * **Joyent, Inc and contributors**: Created an http library called [http-parser](https://github.com/nodejs/http-parser). Located at `lib/http_parser.(c|h)`. License: MIT
 * **Google, Inc and contributors**: Created an implementation of curve 25519 called [curve25519-donna](https://github.com/agl/curve25519-donna). Located in the `lib/curve25519` folder. License: 3-Clause BSD
 * **Team XBMC**: Managed to show a black background for OpenMAX video rendering. This code is used in the video renderer. License: GNU GPL

lib/CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.4.1)
-include_directories( curve25519 ed25519 playfair plist/plist )
+include_directories( curve25519 ed25519 playfair )
 
 aux_source_directory(. play_src)
 set(DIR_SRCS ${play_src})
@@ -9,12 +9,14 @@ add_library( airplay
         ${DIR_SRCS}
         )
 
+find_library( LIBPLIST plist )
+
 target_link_libraries( airplay
 	    pthread
         curve25519
         ed25519
         playfair
-        plist )
+        ${LIBPLIST} )
 
 if( UNIX AND NOT APPLE )
   find_package(OpenSSL REQUIRED)