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.
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/.
Need to wait for the low-level USB driver to send the data over the USB
in-endpoint before the buffer can be used again. This patch adds a
check for this.
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).
Late USB enumeration could clear settings after they had been set.
Now fixed by not clearing some settings on init.
RX was blocking if received characters were not being processed, so
CTRL-C would not be picked up. Now "fixed" by not blocking, but
instead discarding incoming characters if they overflow the buffer.
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...).
