C's printf will pad nan/inf differently to CPython.  Our implementation
originally conformed to C, now it conforms to CPython's way.

Tests for this are also added in this patch.

Saves around 120 bytes on Thumb2 archs.

This allows pyboard.py to be used over a UART interface
rather than just over a USB serial interface.

Now all stmhal-based boards can name their peripherals (if they want) to
any string.

This gets uPy readline working with unix port, with tab completion and
history.  GNU readline is still supported, configure using
MICROPY_USE_READLINE variable.

I have seen the CC3200 hanging a couple of times, and according to TI
itself the SOC reset is not reliable, which explains my observations.

Initializing too early caused some of the API functions (wifi_*) to fail
when called in main.py

Currently implements only .uname()

In general the changes are:

1. Peripheral (UART, SPI, ADC, I2C, Timer) IDs start from 1, not zero.
2. Make I2C and SPI require the ID even when there's only one bus.
3. Make I2C and SPI accept 'mode' parameter even though only MASTER
   is supported.