README: Add USB VID/PID to dfu-util command.

This reflects how it's done in stmhal/Makefile, via deploy.
stmhal: Change 0:/ and 1:/ to /flash and /sd; add CWD support.

Some important changes to the way the file system is structured on the
pyboard:

1. 0: and 1: drive names are now replaced with POSIX inspired
directories, namely /flash and /sd.

2. Filesystem now supports the notion of a current working directory.
Supports the standard Python way of manipulating it: os.chdir and
os.getcwd.

3. On boot up, current directory is /flash if no SD inserted, else /sd
if SD inserted.  Then runs boot.py and main.py from the current dir.
This is the same as the old behaviour, but is much more consistent and
flexible (eg you can os.chdir in boot.py to change where main.py is run
from).

4. sys.path (for import) is now set to '' (current dir), plus /flash
and /flash/lib, and then /sd and /sd/lib if SD inserted.  This, along
with CWD, means that import now works properly.  You can import a file
from the current directory.

5. os.listdir is fixed to return just the basename, not the full path.

See issue #537 for background and discussion.
Fix modos.c to compile for the STM32F4Discovery board (which doesn't have an sdcard)
Merge pull request #781 from dhylands/fix-disc

Fix modos.c to compile for the STM32F4Discovery board
stmhal: Add preliminary driver for ST32F4DISC accelerometer.

Written in Python, not currently working.  See issue #725.
stmhal: Add documentation for LCD; update docs for USB_VCP.
stmhal: Add more documentation for USB_VCP.
Fix teensy to work with the latest tree.
Merge pull request #784 from dhylands/fix-teensy-2014-08-02

Fix teensy to work with the latest tree.
stmhal: Document behaviour of usb_vcp_recv_byte.
Updated teensys usb.c and switched to using usb.h from stmhal.

Removed the local usb.h from teensey directory and now uses
the usb.h from the stmhal directory.
Fixed the deploy target to use abspath.
Merge pull request #786 from dhylands/fix-teensy-2014-08-03

Updated teensys usb.c and switched to using usb.h from stmhal.
Put call to qstr_init and mp_init_emergency_exc_buf in mp_init.

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).
stmhal: Clean up reset/soft-reset code; fix bug init'ing VCP exc.

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.
Merge branch 'master' of github.com:micropython/micropython
Follow rename of readline_init to readline_init0 on teensy
Merge pull request #789 from dhylands/fix-teensy-2014-08-04

Follow rename of readline_init to readline_init0 on teensy
travis: Build stmhal/ST32F4DISC and teensy in Travis tests.
stmhal, math: Define _M_LN2 if not already defined.

Addresses issue #790.
stmhal: Wrap DAC module and os.urandom in relevant #if's.