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.
Pasting more or less sizable text into ESP8266 REPL leads to random chars
missing in the received input. Apparent cause is that using RTOS messages
to pass individual chars one by one is to slow and leads to UART FIFO
overflow. So, instead of passing chars one by one, use RTOS msg to signal
that input data is available in FIFO, and then let task handler to read
data directly from FIFO.
With this change, lost chars problem is gone, but the pasted text is
truncated after some position. At least 500 chars can be pasted reliably
(at 115200 baud), but 1K never pastes completely.
This enables proper interfacing with underlying OS - MicroPython doesn't
run the main loop, OS does, MicroPython just gets called when some event
takes place.
