tools/pydfu.py is now the recommended way of deploying a DFU file.  Old
behaviour of dfu-util can be obtained by passing USE_PYDFU=0 when invoking
make.

The main README.md file has been updated to reflect this change.

Now, all output has newlines converted to \n, regardless of port or
platform.

Also explicitly name the py/*.o files in the linker file, to enable easy
testing of putting certain ones in iRAM.

None of the other ports do, since introduction of mp_state_ctx_t. In
the case of current esp8266 port, heap is inside BSS, so scanning it
picked up a lot of dead pointers.

To make it easier to spot differences.

Useful for embedded targets with fixed stack layout.

NameError may either include offending name or not. Unfortunately, this
change makes test float-dependent. And using integer division leads to
different error message than CPython.

GPIO16 is actually special-function I/O, though some boards have LED there.

OPEN_DRAIN is of course synthesised.  All pin modes are tested and
working.

Enabling standard assert() (by removing -DNDEBUG) produces non-bootable
binary (because all messages go to .rodata which silently overflows).
So, for once-off debugging, have a custom _assert().