Artwork caching (pull request #61), and also:

- introduced new section in config file for sqlite pragma settings,
added config for artwork cache
- added setting of pragma synchronous, cache size and journal mode to
daap cache

src/cache.h

@@ -0,0 +1,54 @@
+
+#ifndef __CACHE_H__
+#define __CACHE_H__
+
+#ifdef HAVE_LIBEVENT2
+# include <event2/event.h>
+# include <event2/buffer.h>
+#else
+# include <event.h>
+#endif
+
+
+/* ---------------------------- DAAP cache API  --------------------------- */
+
+void
+cache_daap_trigger(void);
+
+int
+cache_daap_get(const char *query, struct evbuffer *evbuf);
+
+void
+cache_daap_add(const char *query, const char *ua, int msec);
+
+int
+cache_daap_threshold(void);
+
+
+/* ---------------------------- Artwork cache API  --------------------------- */
+
+int
+cache_artwork_ping(char *path, time_t mtime);
+
+int
+cache_artwork_delete_by_path(char *path);
+
+int
+cache_artwork_purge_cruft(time_t ref);
+
+int
+cache_artwork_add(int64_t persistentid, int max_w, int max_h, int format, char *filename, struct evbuffer *evbuf);
+
+int
+cache_artwork_get(int64_t persistentid, int max_w, int max_h, int *cached, int *format, struct evbuffer *evbuf);
+
+
+/* ---------------------------- Cache API  --------------------------- */
+
+int
+cache_init(void);
+
+void
+cache_deinit(void);
+
+#endif /* !__CACHE_H__ */