mingw: Add implementation of realpath()

RTC doc fix

You can run a local script on the pyboard using:

    python pyboard.py test.py

where test.py is the local script you want to run.

Since firmware lives in a build directory which already specifies the
board name, no real reason to also have the firmware have the board
name.

BUILD is build-$(BOARD) by default.

This renames MICROPY_HW_HAS_WLAN to MICROPY_HW_ENABLE_CC3K (since it's a
driver, not a board feature) and wraps all CC3000 code in this #if.
It's disabled for all boards.

This follows up 0a7e01ae.

In tests/pyb is now a suite of tests that tests the pyb module on the
pyboard.  They include expected output files because we can't run
CPython on the pyboard to compare against.

run-tests script has now been updated to allow pyboard tests to be run.
Just pass the option --pyboard.  This runs all basic, float and pyb
tests.  Note that float/math-fun.py currently fails because not all math
functions are implemented in stmhal/.

The mingw port used _fullpath() until now, but the behaviour is not exactly
the same as realpath()'s on unix; major difference being that it doesn't
return an error for non-existing files, which would bypass main's error
checking and bail out without any error message.

Also realpath() will return forward slashes only since main() relies on that.

CPython compatibility: raise an error for operations on a closed file de...

A negative ms/us is now treated as a delay of 0 ms/us.  This patch also
improves the calibration of udelay.

More relaxed parsing of preprocessed qstr header

Make include dependencies neater, and adheres to the coding convention
that headers should not include headers.

Make pyboard.enter_raw_repl more robust

In CPython any operations on a file that has been closed already reaises
a ValueError with message "I/O operation on closed file"

py: Use <alloca.h> for alloca()

mingw: Add 'open' as extra builtin

Ignore .exe files

Well, it is bound to "detailed error reporting", but that's closest what we
have now without creating new entities.

This one was probable missed when creating mpconfigport.h, but the underlying
code (file.c) gets compiled and works perfectly so no reason to omit it.

The original parsing would error out on any C declarations that are not typedefs
or extern variables. This limits what can go in mpconfig.h and mpconfigport.h,
as they are included in qstr.h. For instance even a function declaration would be
rejected and including system headers is a complete no-go.
That seems too limiting for a global config header, so makeqstrdata now
ignores everything that does not match a qstr definition.

alloca() is declared in alloca.h which als happens to be included by stdlib.h.
On mingw however it resides in malloc.h only.
So if we include alloca.h directly, and add an alloca.h for mingw in it's port
directory we can get rid of the mingw-specific define to include malloc.h
and the other ports are happy as well.

Fix PB0 ADC typo.

Add device ID to autoflash script.