A standard I2C address is 7 bits but addresses 0b0000xxx and 0b1111xxx
are reserved.  The scan() method is changed to reflect this, along with
the docs.

Fixes build under MacOSX.

Per current CPython docs conventions, arguments are in italics. Follow
that.

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.

Request for password then becomes mandatory part of the protocol.

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

That's production setting. Also, extra UART output may affect behavior of
(subpar) network drivers.

Like ESP8266 has.

The smaller chunks we send (and receive), the more packets there to
receive, and higher chance to git internal packet buffer overflow in
WiFi driver.

On PYBLITEv1.0 there is no accelerometer and in this case the Accel()
constructor should not silently succeed.

So detailed that even commented by default.

A bit of optimization.

EAGAIN should be returned only if underlying socket returned it. Wrap
existing read function into external loop to process all data available.

While just a websocket is enough for handling terminal part of WebREPL,
handling file transfer operations requires demultiplexing and acting
upon, which is encapsulated in _webrepl class provided by this module,
which wraps a websocket object.