[hxcpp] implement process_kill

std/cpp/NativeProcess.hx

@@ -33,6 +33,9 @@ extern class NativeProcess
    @:native("_hx_std_process_pid")
    public static function process_pid(handle:Dynamic) : Int return 0;
 
+   @:native("_hx_std_process_kill")
+   public static function process_kill(handle:Dynamic) : Void { };
+
 
    @:native("_hx_std_process_close")
    public static function process_close(handle:Dynamic) : Void { };

std/cpp/_std/sys/io/Process.hx

@@ -115,7 +115,7 @@ class Process {
 	}
 
 	public function kill() : Void {
-		throw "Not implemented";
+		NativeProcess.process_kill(p);
 	}
 
 }