Add (very experimental) FS.h for File & Dir base classes

teensy3/FS.h

+/* Experimental File & Dir base classes.  VERY experimental!
+
+   These are intended to someday allow libraries using files,
+   such as a JPEG decoder, to accept a File object from SD,
+   Bridge, USB Host, ESP SPIFFS, and others.  Perhaps only a
+   distant dream at this point, but maybe someday....
+*/
+
+
+#ifndef FS_H
+#define FS_H
+#ifdef __cplusplus
+
+#include "Stream.h"
+#include "WString.h"
+
+class File : public Stream {
+public:
+	constexpr File() {}
+	enum SeekMode {
+		SeekSet = 0,
+		SeekCur = 1,
+		SeekEnd = 2
+	};
+	virtual size_t read(void *buf, size_t nbyte);
+	virtual size_t write(const void *buf, size_t size);
+	virtual int available();
+	virtual int read();
+	virtual int peek();
+	virtual void flush();
+	virtual bool seek(uint32_t pos, int mode);
+	virtual uint32_t position() const;
+	virtual uint32_t size() const;
+	virtual void close();
+	virtual operator bool() const;
+	//virtual const char* name() const; // why does ESP have this in File?
+
+	bool seek(uint32_t pos) {
+		return seek(pos, SeekSet);
+	}
+	size_t write(uint8_t b) {
+		return write(&b, 1);
+	}
+	size_t write(const char *str) {
+		return write(str, strlen(str));
+	}
+	size_t readBytes(char *buffer, size_t length) {
+		return read(buffer, length);
+	}
+
+	// needed for compatiblity with Arduino's SD & Bridge libs
+	virtual const char* name();
+	virtual bool isDirectory();
+	virtual File openNextFile(uint8_t mode=0);
+	virtual void rewindDirectory(void);
+};
+
+class Dir {
+public:
+	constexpr Dir() {}
+	virtual const char *name(); // from SD's File (and ESP's File)
+	virtual uint32_t fileSize();
+	virtual bool isDirectory(); // from SD, not in ESP
+	virtual File openFile(const char *mode);
+	virtual bool next();
+	String fileName() {
+		return String(name());
+	}
+};
+
+#endif // __cplusplus
+#endif // FS_H