There was a stray factor of 2 (VBAT_DIV) that looks like it was copied incorrectly from the read_core_vbat() function.
The factor exists in read_core_vbat() because VBAT is measured through a 2:1 voltage divider.
read_core_vref now returns values around 1.21V (assuming that external reference voltage is 3.3V) which is in line with the datasheet values.
See comment at http://forum.micropython.org/viewtopic.php?f=6&t=533&p=2991#p2991

Addresses issue #1097.

Also fix list.sort so it works with user-defined types, and parse the
keyword arguments properly.

Addresses issue #338.

Just always keep jumper in bootloader position. After flashing, uPy
automatically executed. And to get back to bootloader, do "make reset".

Only noticeable difference is how newlines are encoded in triple-quoted
strings.  The behaviour now matches CPython3.

Used gcov to find some parts of vm.c, runtime.c, obj.c that were not
covered by any tests.  Still need to use gcov more thoroughly.

Addresses issue #1014.

This cleans up vstr so that it's a pure "variable buffer", and the user
can decide whether they need to add a terminating null byte.  In most
places where vstr is used, the vstr did not need to be null terminated
and so this patch saves code size, a tiny bit of RAM, and makes vstr
usage more efficient.  When null termination is needed it must be
done explicitly using vstr_null_terminate.

Makes pyexec.c more re-usable for other ports.

- This then provides support for floats in the struct package

Eg, "() + 1" now tells you that __add__ is not supported for tuple and
int types (before it just said the generic "binary operator").  We reuse
the table of names for slot lookup because it would be a waste of code
space to store the pretty name for each operator.

Actually manage size of the output buffer.

Defining NDEBUG (to any value, even 0) disables debugging.  Otherwise,
if it's not defined, debugging is enabled.

So far implements .scan(lambda x: print(x)) function to scan for WiFi access
points.