add a quadrature encoder pio example

[pmarques-dev]

No description provided.

[kilograham]

@Wren6991 can you take a look at this
@pmarques-dev this will be added under our BSD-3 license, ok?

[pmarques-dev]

sure, the BSD-3 license is perfectly fine

[kilograham]

I'm assuming this works!

[kilograham]

I put you as (C) pmarques-dev @ github.
Let me know if you'd like something else

[pmarques-dev]

I've tested the code with an actual encoder and it works great. Since it uses a state machine to count the steps, it doesn't miss a step, even in scenarios with frequent changes of direction (like would happen with simpler approaches, like waiting for a specific transition in one phase and using the other phase to decide if it is positive or negative).
Also, since everything is done in the PIO itself it uses zero CPU time to keep track of the count and supports very high step frequencies (unlike what would happen in an interrupt based approach, or if the PIO would send data at each step). The CPU just needs to ask for the current count when it needs it.

[pmarques-dev]

"(C) pmarques-dev @ github" is fine. In the future, If you would prefer to use my real name is "Paulo Marques".
I also have some code to do a full duplex UART on a single PIO, that would allow a RP2040 to have 10 full duplex UARTs, but I haven't had a chance to test it thoroughly yet, so I haven't tried to push it.