Now you can assign to the range variable within the for loop and it will
still work.

Partially addresses issue #565.

Issue was with uPy: on local machine with micropython-lib installed, io
module is available.  Not the case on Travis CI, where only _io module
is available in uPy.

TODO: Figure out what's wrong on Travis.

It's used by stmhal, but not unix.

This patch adds a configuration option (MICROPY_CAN_OVERRIDE_BUILTINS)
which, when enabled, allows to override all names within the builtins
module.  A builtins override dict is created the first time the user
assigns to a name in the builtins model, and then that dict is searched
first on subsequent lookups.  Note that this implementation doesn't
allow deleting of names.

This patch also does some refactoring of builtins code, creating the
modbuiltins.c file.

Addresses issue #959.

This is useful if you need precise control over the speed of
peripherals (eg SPI clock).

The function is modeled after traceback.print_exception(), but unbloated,
and put into existing module to save overhead on adding another module.
Compliant traceback.print_exception() is intended to be implemented in
micropython-lib in terms of sys.print_exception().

This change required refactoring mp_obj_print_exception() to take pfenv_t
interface arguments.

Addresses #751.

Remove include of stm32f4xx_hal.h, replace by include of MICROPY_HAL_H
where needed, and make it compile without float support.  This makes
these 3 modules much more generic and usable by other ports.

Uses DMA if interrupts are enabled, polling if they are disabled.

mp_obj_int_get_truncated is used as a "fast path" int accessor that
doesn't check for overflow and returns the int truncated to the machine
word size, ie mp_int_t.

Use mp_obj_int_get_truncated to fix struct.pack when packing maximum word
sized values.

Addresses issues #779 and #998.

mp_lexer_t type is exposed, mp_token_t type is removed, and simple lexer
functions (like checking current token kind) are now inlined.

This saves 784 bytes ROM on 32-bit unix, 348 bytes on stmhal, and 460
bytes on bare-arm.  It also saves a tiny bit of RAM since mp_lexer_t
is a bit smaller.  Also will run a bit more efficiently.

This patch overhauls the network driver interface.  A generic NIC must
provide a set of C-level functions to implement low-level socket control
(eg socket, bind, connect, send, recv).  Doing this, the network and
usocket modules can then use such a NIC to implement proper socket
control at the Python level.

This patch also updates the CC3K and WIZNET5K drivers to conform to the
new interface, and fixes some bugs in the drivers.  They now work
reasonably well.

Behaviour of array initialisation is subtly different for bytes,
bytearray and array.array when argument has buffer protocol.  This patch
gets us CPython conformant (except we allow initialisation of
array.array by buffer with length not a multiple of typecode).

This makes no change to the generated code, but it's now easier to
understand since unum is not a "global" variable anymore.

So can remove unnecessary stm32f4xx_hal_msp.c file.