Assignments of the form "_id = const(value)" are treated as private
(following a similar CPython convention) and code is no longer emitted
for the assignment to a global variable.

See issue #2111.

Requires a link of the form: <BASEURL>/<lang>/<ver>/micropython-<port>.pdf

By design, at wake up from deepsleep, the RTC timer will be reset, but
the data stored in RTC memory will not [1]. Therefore, we have to adjust
delta in RTC memory before going into deepsleep to get almost correct
time after waking up.

[1] http://bbs.espressif.com/viewtopic.php?t=1184#p4082

Instead of calling strlen(), which won't work if there're 32 chars in
returned ESSID. struct bss_info::ssid_len is not documented in SDK API
Guide, but is present in SDK headers since 1.4.0. Just in case, previous
code is left commented.

To work on a variety of ports the selection of N is very specific.

ESP-SDK system_get_rtc_time() returns uint32 and therefore overflow
about every 7:45h.  Let's write the last state of system_get_rtc_time()
in RTC mem and use it to check for overflow. This commit require running
pyb_rtc_get_us_since_2000() at least once within 7 hours to avoid
overflow.

Makes it work on the ESP8266.

This makes the test reliably overflow the recursion limit (which is the
correct behaviour) on Mac OS X.

And will normalize them.

WebREPL is much more stable now.

This introductions makes explicit the fact that whenever possible,
the documentation describes full MicroPython functionality, and arbitrary
functions/classes/modules may be missing in a paricular port or build.

Using remote image causes problems with tools (partly because the image
is semi-firewalled and can't be accessed by arbitrary tools).

So ets_loop_iter is now only disabled when using machine.disable_irq.

So that RTC.memory() returns b'' on power up if it was never set.

Fixes issue #2138.

This implementation makes use of vfs.stat() and therefore has the same
properties. Known issues for all ports: uos.stat(".") on the top level
returns the error code 22, EINVAL. The same happens with
uos.stat("dirname/") where dirname IS the name of a directory.

Since not all ports that enable the machine module have the pin HAL
functions.

The C implementation is taken from the DHT driver.

The call to stat() returns a 10 element tuple consistent to the os.stat()
call. At the moment, the only relevant information returned are file
type and file size.

This is not part of public API, variable name may change, or it can be
replaced with a function.