Design: Put in idle queue information

This is needed for scheduling files to load later.

Signed-off-by: Bryan Schumaker <bjschuma@gmail.com>

design.txt

@@ -24,6 +24,7 @@ Files:
 		file.h
 		filter.h
 		group.h
+		idle.h
 		index.h
 		library.h
 		playlist.h
@@ -35,6 +36,7 @@ Files:
 		database.cpp
 		file.cpp
 		group.cpp
+		idle.cpp
 		index.cpp
 		library.cpp
 		playlist.cpp
@@ -119,6 +121,47 @@ Audio: (lib/audio.cpp)
 
 
 
+Idle queue: (lib/idle.cpp)
+	The idle queue is used to schedule tasks to run at a later time.  Idle
+	tasks must inherit from the IdleBase class so that multiple templated
+	types can be placed on the same idle queue.
+
+- IdleBase:
+	class IdleBase {
+		IdleBase();
+		~IdleBase();
+		virtual void run() = 0;
+	};
+
+- IdleTask:
+	template <class T>
+	class IdleTask : IdleBase {
+	private:
+		void (*func)(T *);
+		T *data;
+
+	public:
+		IdleTask(void (*)(T *), T *);
+		void run();
+	};
+
+- Queue:
+	deque(IdleTask *> idle_queue;
+	float queued = 0.0
+	float serviced = 0.0
+
+- API:
+	template <class T>
+	void idle :: schedule(void (*)(T *), T *);
+		Schedule a function to run later.
+		queued++
+	bool idle :: run_task()
+		Run the next task on the queue.  Return true if a task was
+		found, and false otherwise.
+		scheduled++, reset to zero if idle queue is empty.
+
+
+
 On-disk files: (lib/file.cpp)
 	I use the disk to store data between sessions, this could include
 	library state and user preferences.  In theory, file formats do not
@@ -243,7 +286,8 @@ Database: (lib/database.cpp)
 		an empty string if you do not want this database to be saved.
 	Database.load();
 		Reads data from file.  Call after static initialization of
-		Ocarina to ensure idle tasks are configured.
+		Ocarina to ensure idle tasks are configured so loading can
+		happen at a later time.
 	Database.save();
 		Saves data to file.
 	Database.insert(T &);