W1401: board support "complete" (update)

The W1401 thermostat board has now initial STM8EF board support, and it's also better documented. There are maybe still some rough edges, but the things I tested work "as expected". It's now part of the "official" release v2.2.7.

• serial interface through PD1/SWIM
• 7S-LED through vectored I/O (auto-off w/ time delay while serial interface active)
• board keys through vectored I/O
• relay/red LED, and green LED through `OUT!`
• buzzer with programmable pitch (`BEEP_CSR` HW-register)
• read sensor input with `5 ADC! ADC@`

The analog input is surprisingly stable: there is just enough noise to get some extra resolution, but one still gets a stable readout down to the LSB without filtering!

The programmable pitch of the BEEP output isn't good enough for playing music (unless you spend extra effort to tuning the RC-oscillator, or if you don't mind annoying people).

The price for a W1401 starts from $2.60/piece (including shipping). It offers a lot of value for the money, especially if you're looking for a hackable board for SISO (Single Input Single Output) control (e.g. thermostat, solar heating, level control, charge control), or for monitoring/safeguarding applications!