stmhal: Fix ptr arith in CC3000 code; enable network build in travis.
py: mp_obj_str_get_str(): Work with bytes too.

It should be fair to say that almost in all cases where some API call
expects string, it should be also possible to pass byte string. For example,
it should be open/delete/rename file with name as bytestring. Note that
similar change was done quite a long ago to mp_obj_str_get_data().
objstr: Allow to convert any buffer proto object to str.

Original motivation is to support converting bytearrays, but easier to just
support buffer protocol at all.
mpz: Fix 64bit msvc build

msvc does not treat 1L a 64bit integer hence all occurences of shifting it left or right
result in undefined behaviour since the maximum allowed shift count for 32bit ints is 31.
Forcing the correct type explicitely, stored in MPZ_LONG_1, solves this.
stmhal: Added support for extended CAN frames.
tests: Added and adapted CAN tests for extended messages
stmhal: Improve CAN print function.
stmhal: Add ioctl to USB_VCP object, so it works with select.

This patch also enables non-blocking streams on stmhal port.

One can now make a USB-UART pass-through function:

def pass_through(usb, uart):
    while True:
        select.select([usb, uart], [], [])
        if usb.any():
            uart.write(usb.read(256))
        if uart.any():
            usb.write(uart.read(256))

pass_through(pyb.USB_VCP(), pyb.UART(1, 9600))
stmhal: Implement support for RTS/CTS hardware flow control in UART.

This is experimental support.  API is subject to changes.  RTS/CTS
available on UART(2) and UART(3) only.  Use as:

    uart = pyb.UART(2, 9600, flow=pyb.UART.RTS | pyb.UART.CTS)
docs: Add tutorial for fading LED using PWM, with fritzing image
docs: Fix links to images and other parts of the docs.
stmhal: Update some inlined docs for network and CAN.
tools: Make gendoc.py able to output RST format.
docs: Import documentation from source-code inline comments.

The inline docs (prefixed with /// in .c files) have been converted to
RST format and put in the docs subdirectory.
docs: Add 2 images for tutorials.
py: Add builtin round function.

Addresses issue #934.
stmhal: Fix UART so bits counts number of data bits, not incl parity.

Addresses issue #950.
py: Make gc.enable/disable just control auto-GC; alloc is still allowed.

gc.enable/disable are now the same as CPython: they just control whether
automatic garbage collection is enabled or not.  If disabled, you can
still allocate heap memory, and initiate a manual collection.
tests: Add heapalloc.py.exp, since CPython can't generate it.
docs: Cleanup and update some docs.