Fixes #795.

Thanks to David Siorpaes.

Similar to other methods and following CPython3 strictness.

This happens for example for zero-size arrays. As .get_buffer() method now
has explicit return value, it's enough to distinguish success vs failure
of getting buffer.

Addresses some issues from #585.

Trying to move towards consistency, let's use _ exclusively in names of
source files (eg .c, .h, .csv).

This was a nasty bug to track down.  It only had consequences when the
heap size was just the right size to expose the rounding error in the
calculation of the finaliser table size.  And, a script had to allocate
a small (1 or 2 cell) object at the very end of the heap.  And, this
object must not have a finaliser.  And, the initial state of the heap
must have been all bits set to 1.  All these conspire on the pyboard,
but only if your run the script fresh (so unused memory is all 1's),
and if your script allocates a lot of small objects (eg 2-char strings
that are not interned).

Converts generted pins to use qstrs instead of string pointers.

This patch also adds the following functions:
pyb.Pin.names()
pyb.Pin.af_list()
pyb.Pin.gpio()

dir(pyb.Pin.board) and dir(pyb.Pin.cpu) also produce useful results.

pyb.Pin now takes kw args.

pyb.Pin.__str__ now prints more useful information about the pin
configuration.

I found the following functions in my boot.py to be useful:
```python
def pins():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin)))

def af():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin.af_list())))
```

Before this patch, eg, 1 << 75 (or any large multiple of 15) was setting
the MSB in the digits, which is outside the valid range of DIG_MASK.

This patch updates ST's HAL to the latest version, V1.3.0, dated 19 June
2014.  Files were copied verbatim from the ST package.  Only change was
to suppress compiler warning of unused variables in 4 places.

A lot of the changes from ST are cosmetic: comments and white space.
Some small code changes here and there, and addition of F411 header.

Main code change is how SysTick interrupt is set: it now has a
configuration variable to set the priority, so we no longer need to work
around this (originall in system_stm32f4xx.c).

Addresses issue #780.

Specifically, teensy port does not have these macros defined.

Addresses issue #790.

Follow rename of readline_init to readline_init0 on teensy

Make a clearer distinction between init functions that must be done
before any scripts can run (xxx_init0) and those that can be safely
deferred (xxx_init).

Fix bug initialising USB VCP exception.  Addresses issue #788.

Re-order some init function to improve reliability of
reset/soft-reset.

qstr_init is always called exactly before mp_init, so makes sense to
just have mp_init call it.  Similarly with
mp_init_emergency_exception_buf.  Doing this makes the ports simpler and
less error prone (ie they can no longer forget to call these).

Updated teensys usb.c and switched to using usb.h from stmhal.