This builds upon the changes made in 2195046365. Using signal() does not
produce reliable results so SetConsoleCtrlHandler is used, and the handler
is installed only once during initialization instead of removing it in
mp_hal_set_interrupt_char when it is not strictly needed anymore, since
removing it might lead to Ctrl-C events being missed because they are
fired on a seperate thread which might only become alive after the handler
was removed.
py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for. A
port will also provide mphalport.h with further HAL declarations.
If VT100 support is not available then a given implementation of
mp_hal_erase_line_from_cursor might need to know the number of characters
to erase.
This patch does not change generated code when VT100 is supported, since
compiler can optimise away the argument.
