Mostly just a global search and replace.  Except rt_is_true which
becomes mp_obj_is_true.

Still would like to tidy up some of the names, but this will do for now.

All board config macros now begin with MICROPY_HW_.

Renamed PYBv10 to PYBV10, since macros should be all uppercase.

Made SDCARD_DETECT configurable in mpconfigport.h, so that the SD
detect pin can be easily configured.

Caught by CPython test_pep380.py.

According to PEP380 and caught by CPython test_pep380.py .

vm: Save current active exception on opening new try block.

Can now choose at boot up whether the USB device is CDC+MSC or CDC+HID.
Choice is made by an option in boot.py, with default being CDC+MSC.
HID+MSC is not currently supported, but should be easy to implement.

Boot up now has ability to change the reset mode: hold down USR switch
while booting and LEDs will count from 1 to 7 to indicate the boot mode.
Release USR when correct mode is selected.  Current modes are 1 (normal
boot), 2 (safe mode), 3 (reset FS mode).

Required to reraise correct exceptions in except block, regardless if more
try blocks with active exceptions happen in the same except block.

P.S. This "automagic reraise" appears to be quite wasteful feature of Python
- we need to save pending exception just in case it *might* be reraised.
Instead, programmer could explcitly capture exception to a variable using
"except ... as var", and reraise that. So, consider disabling argless raise
support as an optimization.

The HID device must appear before the CDC in order for both to work at
the same time.

Whilst the code is working, it's not currently used.

E.g. to handle currently_in_except_block restoring properly.

Adds readline_init() to clear readline history on soft reset.  Addresses
issue #387.

The compiler allocates 7 entries on the stack for a with statement
(following CPython, but probably can be reduced).  This is enough for
the method load and call in SETUP_WITH.

With statement implementation

Addresses issue #388.

Implement "yield from"

Partly (very partly!) addresses issue #386.  Most importantly, at the
REPL command line, each invocation does not now lead to increased memory
usage (unless you define a function/lambda).

This reduntant triple is one of the ugliest parts of Python, which they
chickened out to fix in Python3. We really should consider passing just
as single exception instance (without breaking Python-level APIs of course),
but until we do, let's follow CPython layout.

Will be reused in WITH bytecodes.