Should fix issue #1393.

In particular this fixes a bug where pyb.sync (and os.sync) fail because
they try to sync the user mounted device even if it's not mounted.

ViperTypeError now includes filename and function name where the error
occurred.  The line number is the line number of the start of the
function definition, which is the best that can be done without a lot
more work.

Partially addresses issue #1381.

Disabled by default.  Adds 108 bytes to Thumb2 arch when enabled.

The adapter class "TelnetToSerial" is used to access the Telnet
connection using the same API as with the serial connection. The
function pyboard.run-test() has been removed to made the module
generic and because this small test is no longer needed.

When looking for chars to indicate raw repl is active, look for the full
string of chars to improve reliability of entering raw repl correctly.

Previous to this patch there was the possibility that raw repl was
entered in a dirty state, where not all input chars from previous
invocation were drained.

Addresses issue #1390.

Otherwise it can be very hard to track down bugs.

Addresses issue #1380.

This allows a user-specified Timer for the triggering of the ADC read,
mirroring the new behaviour of DAC.write_timed.

Addresses issue #1129.

This allows the DAC to use a user-specified Timer for the triggering
(instead of the default Timer(6)), while still supporting original
behaviour.

Addresses issues #1129 and #1388.

This prevented pin_find_af* functions from being able to find some
of the alternate functions in the pin struct

Also adds #if guards to allow uPy core to compile without memoryview
enabled, but with slice assignment enabled.

Adds ability to do "memcpy" with memoryview objects, such as:
m1[0:3] = m2[2:5].

Only those files which are needed by the stmhal port are added.

Also includes a dummy file (stm32f2xx_hal_pcd_ex.c) to keep the build
system the same for f4 and f2 MCU series.

This is in preparation for supporting other MCU series, such as
STM32F2xx.  Directory structure for the HAL is now hal/f4/{inc,src},
where "f4" will in the future be different for other series.

HAL source/header files that are not use are removed to reduce the size
of the code.

This patch makes configurable, via MICROPY_QSTR_BYTES_IN_HASH, the
number of bytes used for a qstr hash.  It was originally fixed at 2
bytes, and now defaults to 2 bytes.  Setting it to 1 byte will save
ROM and RAM at a small expense of hash collisions.

TODO: Contributed code in modesp incorrectly uses private gc_* API.

Simplelink's socket send checks for the size of the packet and sends
it in chunks if the size is too large.