Windows MSVC port

Extend the windows port so it compiles with the toolchain from Visual Studio 2013
py, compiler: Add basic support for A=const(123).

You can now do:

    X = const(123)
    Y = const(456 + X)

and the compiler will replace X and Y with their values.

See discussion in issue #266 and issue #573.
Merge pull request #568 from stinos/windows-msvc-port

Windows MS Visual C port
stmhal: Add time.time() and time.localtime().

time.time: returns seconds since 1/1/2000, as an integer.

time.localtime: Returns 8-tuple: (year, month, date, hour, minute,
    second, weekday, yearday).
Add gc.enable, gc.disable; remove pyb.gc.
README: Add short overview of Python features supported.

Also, "upgrade" project to "early beta", and elaborate pyboard description.
README: Add articles, and update doc for deploying firmware.
Merge branch 'pfalcon-README-features-overview'
windows: Add modtime implementation