Should allow to diagnose/try to recover FS easier.

websocket_helper.py is used by webrepl.  If webrepl is enabled and
websocket_helper.py is not frozen bytecode it leads to heap
fragmentation.

The NeoPixel class now handles 4 bytes-per-pixel LEDs (extra byte is
intensity) and arbitrary byte ordering.  APA102 class is now derived from
NeoPixel to reduce code size and support fill() operation.

The OneWire class is now in its own onewire.py module, and the temperature
sensor class is in its own ds18x20.py module.  The latter is renamed to
DS18X20 to reflect the fact that it will support both the "S" and "B"
variants of the device.

These files are moved to the modules/ subdirectory to take advantage of
frozen bytecode.

That apparently will only help folks who read the docs on how to disable,
but could use a quick reminder straight in boot.py. For the developers,
it's important to have debug logging enabled in development branch
(master).

Leads to less fragmentation at teh time user code starts.

To start with, the critical scripts _boot.py and flashbdev.py are frozen
to improve performance and reduce RAM consumption.

Saves about 1000 bytes of heap RAM for a bare boot with filesystem.

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

TODO: should go in a more port-neutral place, like drivers/dht, but at the
moment in relies on specific esp module.

APA102 is a new "smart LED", similar to WS2812 aka "Neopixel".

modwebrepl truncates password to 9 chars, and that led people to confusion.

That was the intent for the initial user setup, but didn't work before
due to lwIP issues. Enable now that they're fixed.

Starts WebREPL server in foreground and waits for (single) connection.

This commit fixes issue #2045

It interferes with running testsuite. master branch should be optimized for
development, so any features which interfere with that, would need to be
disabled by default.

This constant is no longer part of hardware API (replaced with just None),
and is a default, so not needed in calls.

.time() returns seconds since MicroPython epoch (2000-01-01 00:00UTC),
.settime() sends current system time, assuming UTC timezone.

If there's no port_config.py file, or it lacks WEBREPL_PASS variable,
"initial setup mode" will be entered on first WebREPLconnection. User
will be asked for password, which will be written to
port_config.WEBREPL_PASS, and system restarted to work in normal mode
with password active.

Handling of binary protocol is untested on esp8266 so far.

After password is checked.

Currently it pre-imports webrepl, but doesn't start it.

It takes up lots of room and isn't needed.

Changes are:
- added OneWireError exception and used where errors can occur
- renamed read/write functions to use same names as C _onewire funcs
- read_bytes is now read, write_bytes is now write
- add ability to read/write DS18B20 scratch pad
- rename start_measure to convert_temp (since that's what it does)
- rename get_temp to read_temp (consistency with other read names)
- removed test function

To remind people it's not HTTP.