Put some code into the first 16K of flash

This basically shrinks the remaining size of flash in the portion
that goes after the internal flash drive.

Also fix unix port so that SystemExit with no arg exits with value 0.

It's still "safe" because no scripts are run.  Remove the SD card if you
want to access the internal flash filesystem.  Addresses issue #616.

Also: remove obsolete pyb.source_dir setting, and reset pyb.main and
pyb.usb_mode settings on soft-reset.

Waiting for 1000ms between seconds of RTC is sometimes too quick.
Waiting for 1001ms is enough for the RTC to pass 1 second.

Saves over 35k ROM due to elimination of unused HAL functions.  All
tests pass.

Addresses issue #702.

Updated teensy/README.md to reflect change in build process (teensyduino is no
longer required for build).

Viper functions can now be annotated with the type of their arguments
and return value.  Eg:

@micropython.viper
def f(x:int) -> int:
    return x + 1

Some small code clean-ups that result in about 80 bytes ROM saving for
stmhal.

msvc: Use built-in alignof

Multiplication of a tuple, list, str or bytes now yields an empty
sequence (instead of crashing).  Addresses issue #799

Also added ability to mult bytes on LHS by integer.

This also fixes a 'unnamed type definition in parentheses' warning on the
alignof implementation define in binary.c

The only change is line-ending convesion to LF.

Also disable gc module on bare-arm port.

Also fixes compiler error in moductypes when compiled without debugging.

Addresses issue #778.

Can now index ranges with integers and slices, and reverse ranges
(although reversing is not very efficient).

Not sure how useful this stuff is, but gets us closer to having all of
Python's builtins.

reversed function now implemented, and works for tuple, list, str, bytes
and user objects with __len__ and __getitem__.

Renamed mp_builtin_len to mp_obj_len to make it publically available (eg
for reversed).

Saves code bytes and makes it faster, so why not?

Fixes #795.

Thanks to David Siorpaes.

Similar to other methods and following CPython3 strictness.