Digital I/O & Analog In - Pi Pico USB

Initial test release for the CTI team to start playing with.

Commands:

DIGital:DIRection <GPIO#>, <IN|OUT>
DIGital:DIRection? <GPIO#>
DIGital[:OUTput]:VALue <GPIO#>, <0|1|OFF|ON>
DIGital[:OUTput]:VALue? <GPIO#>
DIGital[:INput]:VALue? <GPIO#>
DIGital[:INput]:PULL <GPIO#>, <NONE|UP|DOWN|BOTH>
DIGital[:INput]:PULL? <GPIO#>

ANAlog[:INput]:ENable <AI#>, <0|1|OFF|ON>
ANAlog[:INput]:VALue? <AI#>