cmdline: support Windows

cmdline: support Windows

Implement terminal handling, input polling, and vdprintf() for Windows.

Because Windows I/O model differs fundamentally from Unix and there is
no concept of character device, polling is simulated depending on the
underlying input device. Supporting non-terminal input is useful for
automated testing.

Windows emulation of VT100 uses "ESC [ E" for newline instead of
standard "ESC E", so add a workaround.

Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>