Moved Discord RPC library's source code to external

Externals/discord-rpc/CMakeLists.txt

@@ -0,0 +1,56 @@
+cmake_minimum_required (VERSION 3.2.0)
+project (DiscordRPC)
+
+include(GNUInstallDirs)
+
+option(BUILD_EXAMPLES "Build example apps" ON)
+
+# format
+file(GLOB_RECURSE ALL_SOURCE_FILES
+    examples/*.cpp examples/*.h examples/*.c
+    include/*.h
+    src/*.cpp src/*.h src/*.c
+)
+
+# Set CLANG_FORMAT_SUFFIX if you are using custom clang-format, e.g. clang-format-5.0
+find_program(CLANG_FORMAT_CMD clang-format${CLANG_FORMAT_SUFFIX})
+
+if (CLANG_FORMAT_CMD)
+    add_custom_target(
+        clangformat
+        COMMAND ${CLANG_FORMAT_CMD}
+        -i -style=file -fallback-style=none
+        ${ALL_SOURCE_FILES}
+        DEPENDS
+        ${ALL_SOURCE_FILES}
+    )
+endif(CLANG_FORMAT_CMD)
+
+# thirdparty stuff
+execute_process(
+    COMMAND mkdir ${CMAKE_CURRENT_SOURCE_DIR}/thirdparty
+    ERROR_QUIET
+)
+
+find_file(RAPIDJSONTEST NAMES rapidjson rapidjson-1.1.0 PATHS ${CMAKE_CURRENT_SOURCE_DIR}/thirdparty CMAKE_FIND_ROOT_PATH_BOTH)
+if (NOT RAPIDJSONTEST)
+    message("no rapidjson, download")
+    set(RJ_TAR_FILE ${CMAKE_CURRENT_SOURCE_DIR}/thirdparty/v1.1.0.tar.gz)
+    file(DOWNLOAD https://github.com/miloyip/rapidjson/archive/v1.1.0.tar.gz ${RJ_TAR_FILE})
+    execute_process(
+        COMMAND ${CMAKE_COMMAND} -E tar xzf ${RJ_TAR_FILE}
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/thirdparty
+    )
+    file(REMOVE ${RJ_TAR_FILE})
+endif(NOT RAPIDJSONTEST)
+
+find_file(RAPIDJSON NAMES rapidjson rapidjson-1.1.0 PATHS ${CMAKE_CURRENT_SOURCE_DIR}/thirdparty CMAKE_FIND_ROOT_PATH_BOTH)
+
+add_library(rapidjson STATIC IMPORTED ${RAPIDJSON})
+
+# add subdirs
+
+add_subdirectory(src)
+if (BUILD_EXAMPLES)
+    add_subdirectory(examples/send-presence)
+endif(BUILD_EXAMPLES)