This patch was needed for gcc 4.4.

These scripts should run under as wide a range of Python versions as
possible.

1. Updated linker script, now user app appears to contain exception vector
table and oesn't work (faults) without it.
2. Commened out support for GPIO pulldown, which was removed in this SDK
version without clear explanation, but apparently because it was released
without proper validation, and now turns out it doesn't work as expected,
or there's a different function there.

I document as much as I could guess from experiments and reading the
code for the ``esp`` module for the ESP8266 port of Micropython.

For now the tag has to be set manually with -t option when building,
when we have properly split documentation, there will be a separate
config file for esp8266 with that the tag "port_esp8266" set.

To build use:

make SPHINXOPTS="-t port_esp8266" html

Default implementation uses VT100-style sequences which are not implemented
by all terminals out there

xterm and others use the ESC[~3 sequence when pressing the delete key

This assures the terminal prints it's prompt on a fresh line instead of
appending it to the uPy prompt after exit.

After switching to builtin readline support, "minimal" no longer builds, and
minimal doesn't really need readline support.

Using MICROPY_PY_SYS_PATH_DEFAULT macro define. A usecase is building a
distribution package, which should not have user home path by default in
sys.path. In such case, MICROPY_PY_SYS_PATH_DEFAULT can be defined on
make command-line (using CFLAGS_EXTRA).

Currently, frozen packages are not supported, but eventually they should be,
so make sure to store complete directory hierarchy.

C's printf will pad nan/inf differently to CPython.  Our implementation
originally conformed to C, now it conforms to CPython's way.

Tests for this are also added in this patch.

Saves around 120 bytes on Thumb2 archs.

This allows pyboard.py to be used over a UART interface
rather than just over a USB serial interface.

Now all stmhal-based boards can name their peripherals (if they want) to
any string.

This gets uPy readline working with unix port, with tab completion and
history.  GNU readline is still supported, configure using
MICROPY_USE_READLINE variable.