- use correct 'mingw-w64' package name
- small grammar fixes
- modify Cygwin build instructions to use that same compiler as well: the
  original mingw is stuck at gcc v4.7 and does not seem to be updated anymore
- make it clear thet uPy also builds using Visual Studio versions > 2013

Reported here: http://forum.micropython.org/viewtopic.php?f=2&t=845

Ubuntu's mingw32 has gcc 4.2.1, which is rather old and has incorrect
non-initialized variable analysis which produces warnings, which
per MicroPython default settings get turned into errors.

Contains implementation of ?: (non-capturing groups), ?? (non-greedy ?),
as well as much improved robustness, and edge cases and error handling by
Amir Plivatsky (@ampli).

Otherwise for code like:

while (socket->incoming == NULL) {
    LWIP_DELAY(100);
}

a compiler may cache it in a register and it will be an infinite loop.

py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for.  A
port will also provide mphalport.h with further HAL declarations.

This makes format specifiers ~ fully compatible with CPython.

Adds 24 bytes for stmhal port (because previosuly we had to catch and report
it's unsupported to user).

This is the case already when using just subprocess.check_output, but in
the special cases (cmdline, meminfo, ...) the carriage return gets lost
during output processing so restore it in the end.
This fixes the micropython/meminfo.py test on Windows.

This fixes the basics/exception_chain.py test, also see #1500 for more
info and [4300c7db] where the same change was done for the other ports.

As per ARM convention.

This prevents the loss of RTC time when exiting from standby mode, since
the RTC is paused while it is being re-inited and this loses about 120ms.

Thanks to @chuckbook for the patch.

Since VS2015, float formatting is C standard compliant by default:
https://msdn.microsoft.com/en-us/library/bb531344(v=vs.140).aspx

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