Before, pyb.stdin/pyb.stdout allowed some kind of access to the USB VCP
device, but it was basic access.

This patch adds a proper USB_VCP class and object with much more control
over the USB VCP device.  Create an object with pyb.USB_VCP(), then use
this object as if it were a UART object.  It has send, recv, read,
write, and other methods.  send and recv allow a timeout to be specified.

Addresses issue 774.

Recent changes to builtin print meant that print was printing to the
mp_sys_stdout_obj, which was sending data raw to the USB CDC device.
The data should be cooked so that \n turns into \r\n.

Still some method names to iron out, and funtionality to add, but this
will do for the first, basic version.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

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.

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).

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.

This gives a functioning, independent MSC device.

New USB HAL is quite a bit improved over previous one.  Now has better
callbacks and flow control.

REPL over USB CDC now works as before, except for soft-reset (since USB
driver uses malloc...).

Enumerates CDC device over USB, but doesn't transmit/receive yet.

With this option selected, only HID on its own works, not VCP+HID.

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

Using PendSV interrupt at lowest priority, code can now raise an
exception during an interrupt by calling pendsv_nlr_jump.  The exception
will be raised when all interrupts are finished.  This is used to trap
ctrl-C from the USB VCP to break out of running Python code.

* Detect VCP line state, based on SET_CONTROL_LINE_STATE request

See pyb_usart_global_debug variable.

Also did some work on USB OTG, but nothing working yet.