added code for mp3 and jpeg parsing

added interface for data sources

data/formats/DataSourceFile.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include "../../ext/sd/File.h"
+
+/** data source using our filesystem */
+class DataSourceFile {
+	
+	File* f;
+	
+public:
+
+	/** empty ctor */
+	DataSourceFile() : f(nullptr) {
+
+	}
+
+	/** ctor with the filesystem file to wrap */
+	DataSourceFile(File& f) : f(&f) {
+		
+	}
+	
+	/** get the current position */
+	uint32_t curPos() const {
+		return f->curPos();
+	}
+
+	/** seek to the given position */
+	void seekTo(uint32_t newPos) {
+		f->seekTo(newPos);
+	}
+
+	/** read x bytes from the input into dst */
+	uint32_t read(uint32_t size, uint8_t* dst) {
+		return f->read(size, dst);
+	}
+
+	/** read an entity */
+	template <typename T> void readType(T& dst) {
+		read(sizeof(T), (uint8_t*)&dst);
+	}
+
+};