Rewrite the I2S code from scratch to eliminate the dependence on the
pico-extras implementation and to support I2S input as well.
8-bit, 16-bit, 24-bit, and 32-bit words are supported.
Multiple I2S ports are allowed (theoretically up to 6 because
2 DMA channels are required per port).
I2S input and I2S output are supported.
Add input example
Fixes#535Fixes#99Fixes#562
Adds code to define which pins are used, moving them from the defaults, which are the same as the only three analogue input pins, and adding comments to explain how to change them.
The original didn't give any clues about which pins were used, which isn't ideal for a beginner - it was necessary to look at the code for the library, to work that out.
The new code redundantly defines a pWS pin number (as pBCLK+1), which isn't used in the example, but is meant as a reminder to the person using it, of how to wire up WS.
