py: Factor out persistent-code reader into separate files.

Implementations of persistent-code reader are provided for POSIX systems
and systems using FatFS.  Macros to use these are MICROPY_READER_POSIX and
MICROPY_READER_FATFS respectively.  If an alternative implementation is
needed then a port can define the function mp_reader_new_file.
diff --git a/py/reader.h b/py/reader.h
new file mode 100644
index 0000000..f39cc90
--- /dev/null
+++ b/py/reader.h
@@ -0,0 +1,45 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2016 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_PY_READER_H
+#define MICROPY_INCLUDED_PY_READER_H
+
+#include "py/obj.h"
+
+// the readbyte function must return the next byte in the input stream
+// it must return MP_READER_EOF if end of stream
+// it can be called again after returning MP_READER_EOF, and in that case must return MP_READER_EOF
+#define MP_READER_EOF ((mp_uint_t)(-1))
+
+typedef struct _mp_reader_t {
+    void *data;
+    mp_uint_t (*readbyte)(void *data);
+    void (*close)(void *data);
+} mp_reader_t;
+
+bool mp_reader_new_mem(mp_reader_t *reader, const byte *buf, size_t len, size_t free_len);
+int mp_reader_new_file(mp_reader_t *reader, const char *filename);
+
+#endif // MICROPY_INCLUDED_PY_READER_H